Will need extra details to answer:

1. What grading report (commonly as certificate)? GIA
2. If GIA, what is the number? 1196288782
3. If not GIA, which lab they use to grade? It’s GIA Certified

HCA score is 3.6: https://www.pricescope.com/tools/hca, so personally, I will skip this stone. The proportions may leak light as well -> Deep cut @ 62.8% total depth.

Calculate the expected weight using the dimensions and 6.33 x 6.39 x 3.99 x 0.0061 = 0.985ct.
The only thing I like about this diamond is the clarity as the inclusions are not on the center of the diamond (the table) and it is only pinpoint and feather. It should be a high VS2.

The fluorescence is strong blue, according to the sales man it will lower the yellowish color of the diamond? <- That's what Brian Gavin Diamonds (affiliate link) always said as well, so I believe that is true.

If you don't want to rely on HCA to help you filter (some may say it is just for reference and can't make the final call), then have a look at the Arrows of this diamond, is it well-aligned? I don't think you can view the Hearts as I believe this diamond is mounted on a ring. If you can view, they by all means view it as well using a Hearts & Arrows scope. All jewellers should have that in-store.

Lastly, do you like what you see?

Here is some diamonds that are close to your budget:
1.026 K VVS2 SIGNATURE BLUE ROUND
https://www.briangavindiamonds.com/diamonds...?a_aid=myengexp (affiliate link)
Price: USD 5288, MYR 21,739.36 (Transfer using MoneyMatch: https://transfer.moneymatch.co/)
Desc: Brian Gavin Diamonds does not sell this as a Hearts & Arrows diamond, but rather as a budget friendly ideally cut diamond. But don't let this put you off because it is pretty hard to find diamonds that are cut to such quality in the mass market.

https://www.whiteflash.com/loose-diamonds/r...id=myengringexp (affiliate link)
1.084 ct K SI1 A CUT ABOVE® Hearts and Arrows Diamond
Price: USD 4615, MYR 18,973.62 (Transfer using MoneyMatch: https://transfer.moneymatch.co/)
Desc: This diamond has great performance based on the actual diamond video. I would recommend you to check it out. The 6 o'clock arrow head and the arrow body seem to misaligned very slightly (if you want to be picky), but that is nothing unusual to me and it is still acceptable. This is an SI1 stone so I won't expect to see it eye-clean with a loupe or see it eye-clean at very close range, like few centimeters from the eyes. However, at a distance of approximately 10 inches under normal overhead lighting, it is definitely eye-clean. This is based on the definition from WhiteFlash. The Hearts and Arrows look very much acceptable as well.

Memory Jewellery setting is usually standard fit and price starts from RM 1499:
https://memoryjewellery.com/category/engagement-ring/
As far as I know, Memory Jewellery won't increase the setting price even if you stone is bigger. It makes sense because there is enough profit margin to cover any differences.

Bad thing about it is that their setting doesn't come with comfort fit as far as I know.

For comfort fit, you can try:
1. iDo Jewellery at Bukit Jalil. Her rings are not bad and she uses palladium in the 18k white gold mix. As gold is yellow in colour, 18k white gold will need whitening agent inside the alloy, so palladium is the whitening agent. In the mass market, usually nickel is the standard. However, nickel may cause allergic to a minor set of people. Nonetheless, if you other half is not sensitive to 18k white gold, then usually not a problem. Her price is usually not the cheapest but quality is there.

2. The Gem Tribe at Cheras: Relatively new player in town. One of the founders have been in this industry for a few years and she is able to provide ring settings as well. Her setting comes in comfort fit as well and her price starts from as low as RM 1200. You can specifically ask for palladium for the 18k white gold. Price may increase though. The final ring price should depend on the ring size, and probably diamond size as well, because logically speaking, bigger rings require more material, as simple as that. So it is a slightly different approach compared to MJ above.

You can ask them to bring some samples to try. iDo Jewellery has some, I believe TGT has too.

Diamond Altnernatives:
You can also ask MJ, iDO, or TGT to give you a quote for your required 4Cs as well, they do help customers to source for diamonds. Other players worth to consider is Tailored Jewel, which might also offer you some attractive price for your specs. Of course, you can also engage ZCOVA (affiliate link) for some other alternatives. Try to make appointment with them and have an experience with them and see.

iDo and TGT prefers to meet outside at a cafe or something. MJ has a showroom in Sentul. Tailored Jewel as a showroom at Atria Shopping Gallery, PJ. ZCOVA has a showroom at Kota Damansara. But, don't expect them to let you see the real diamond. They don't keep stock, as they run on virtual inventory. They will help you to source the best diamond for your budget through their respective sources.

GIA has its own pros and cons, just like any other labs, but it is still the world's most recognized lab. As simple as that.

IGI is priced higher? I believe those diamonds you saw belongs to a "branded" line. As far as my memory serves me well, I rmb previously Love & Co signature line is using IGI, Diamonds and Platinum's Estrella is using IGI, Suen's Love Diamonds is using IGI. All these are considered stones that are being marketed as top-tier stones hence you have the "feeling" of being more expensive. They are sent to be graded by IGI  probably because they are slightly cheaper than GIA (I could be wrong).

GIA being sold in brick-and-mortar are mostly non-branded stones. Of course, they are some, like Le Lumiere (can be found in Tomei, My Diamond. Gold Heart -> Under same roof).

Personally, I will buy a decently cut GIA stone compared to a branded cut IGI stone because at the end of the day, it is still a 57-facet round brilliant diamond. Is a matter of who has the better 4Cs, proportions, and precision.

On man-made diamonds. IGI and GIA both grades lab grown diamonds. But their report will be a different type. So if you see the standard report, it will be natural

The stones have listed are SI1s stones. Are you asking whether you should go for those?

As for Emerald? Their performance is not as good as round, so I won't really suggest it.

Rmb that carat weight does not mean the size will be bigger. A badly cut diamond can actually look smaller than better cut diamonds.

How about buying shy of 0.7ct? You can get higher colour, higher clarity, and at the same time, close enough to a 0.7ct, and most importantly, close to your budget.:
https://www.hpdiamonds.com/en-us/diamonddetail/HPD10354

The proportions look nice. But it is a 2015 stone... wonder why it is still there. 

Anyway, proportions is one thing, as the numbers are just an average number based on measurement from various angles, it cannot be used to determine how good the cut is. Did you manage to see the "Arrows" on the diamond?

Also, what is the price the quoted you?

As for small or not, it is really not up to me to say, it is really up to each individual preference and budget.

Anyway, this looks pretty decent: https://enchanteddiamonds.com/diamonds/view/R81-803476731?

And I know this stone's supplier (coincidentally). The supplier rated this stone's Hearts & Arrows at 90% accuracy. For the colour, clarity, and size, I think it is worthy for consideration.

I won't mind the Faint fluorescence because it has negligible effect on a stone's appearance. And it can also help to reduce the stone price a little.

So where can you get this stone?
1. Memory Jewellery - RM18,116.00 (Negotiable, they do ring setting too)
2. Tailored Jewel - RM19,109.01 (Should be negotiable, they do ring setting too)
3. Enchanted Diamonds  - RM 16,961.67 (After converting USD to MYR, they do ring setting too, but I won't recommend do it overseas for resizing purpose)
4. ZCOVA - They can possibly price match the cheapest on the list on top (They do ring setting too)
.
.
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5. Me - I can even get it for you if you trust me, you will get the stone in raw parcel paper. I can possibly get it for you for RM 15,800. And at the same time, I am still earning some profit. But then, you have to think about it. I don't provide any extra service, so most people won't be comfortable about it. And you can only verify the stone at the jeweler because I don't have any girdle viewer for you to see. So this is the risk.

Anyway, these are your options. And I find that this stone seems to be value for money and not too shabby.

Wah Chan is filtering out based on proportions, you know. Those numbers on The GIA report. They claim to be Hearts and Arrows too, which I think it will exhibit some sort of Hearts and Arrows pattern in this case here. How good it is, is rather subjective as grading labs do not grade Hearts and Arrows precision.

As for whether the stone sparkles or not? I am sure it will, but again, if you want to look at the stone physically, then this idea is not for you. If you want physical store shopping, I would suggest you to drop by Le Lumiere at the Gardens to compare with their Hearts and Arrows. You can also visit any DeGem to view their Lazare diamonds too.

And for that price, you can get this https://black.briangavindiamonds.com/diamon...?a_aid=myengexp (affiliate link). Performance? I am pretty sure this stone will be excellent, and at the same time, providing you the best cut quality possible. In terms of sparkles, you won't be disappointed with that. This is the sort of diamond that provides you eye-clean, mind-clean, and performance guaranteed performance. So yes, I am quite confident that this diamond will be compatible to the stone you see, if not better. And as far as cut quality is concerned, Brian Gavin shows you everything. How precise it is etc. And how great the light return is. So, if I am paying that amount, I would be getting this instead.

And to maximize on budget, I would consider this: https://www.whiteflash.com/loose-diamonds/r...id=myengringexp (affiliate link). It will be approximately RM 13851.51. WhiteFlash ACA are fully-vetted by their in-house gemologist and they are guaranteed to be eye-clean at normal viewing range. And if you see the enlarged image of the diamond, you will also see it is pretty eye-clean already. So I would say this is a good stone for the budget.

On the Other Hand
You can actually contact ZCOVA to find out more options. They have extensive connection to various suppliers in the world. Imagine them as BlueNile, the largest online diamond reseller. But since BlueNile does not ship to Malaysia, ZCOVA is your best bet. One of the founder is a GIA Graduate Gemologist and he should be able to provide you a sound advice on your options available. Again, they are not holding any in-house diamonds as far as I know, but all their diamonds are based on videos and photographs from respective suppliers.

You can also contact Shannon from The Gem Tribe. Find them on Facebook or Instagram. She sources stones locally with some local suppliers and compare them side-by-side in real time. She will then let you know your options as well as any info related. She is different than others because she can actually see the diamonds herself, instead of relying on videos or photographs. So this is one of the key strength of her company. And I also like her ring settings, they look pretty nice and well crafted.

On a Side Note
Most people like colours on the higher colour scale, like D,E,F. But if you want to maximize on budget, G colour is actually pretty good. It is basically indistinguishable from a higher colour diamond when facing-up. This is because the colour of the diamodn will usually be located at the body, or the side of the diamond, and G colour itself is actually pretty white on its own. They can be more obvious if there is another higher colour diamond comparing with them side-by-side. So do think about it.

As for clarity, to me, my sweet spot is VS1. VS2 can be hit-or-miss sometimes, but usually is a hit. So yea, VS1 is my sweet spot. VS2 we can go case-by-case basis. SI1, same, case-by-case, but hitting the right one will save quiet a bit of money.