OK, time for me to contribute 1 lengthy review since I got my chair now

My own stature: 165cm, normal BMI
Sihoo M57 (black with legrest)
Price: RM829 (originally priced RM859)
I found this seller via Shopee/Lazada, then went to their store as they offered test sit (on rejected units). They offered a minor discount that will be applicable on 12.12, on top of that free delivery and installation.
In hindsight, it is better to just buy from them online because:
1. you will be able to use the platform's vouchers, securing a much cheaper deal.
2. they still offer free delivery nonetheless.
3. In case of seller issues, you have the platform as a leverage to get refunds.
I'm just self-consoling at this point that I didn't have to install the whole thing myself

Alternatively, there are other better sellers.
» Click to show Spoiler - click again to hide... «
I went to them late Nov and paid on the spot after testing. I later realised that their online sales was cheaper because they still offered 11.11 voucher at RM50 discount (20 bucks cheaper than what I got), valid till 30 Nov. I notified them saying they offered a discount too little for me, showing the voucher on platform. They apologised, and then RETRACTED the voucher and thanks me. I was looking for a little rebate on top of my purchase or simply anything from the seller, but instead I end up feeling tad bit bitter about this transaction, even though they did deliver and install it for me as promised. I acknowledge this is my own mistake for jumping the gun, but I felt they could have handled this situation better to earn themselves a better reputation. Just leaving this comment here as a lesson to self (to be more consumer-aware), and to the sellers to take note of customer's satisfaction. It is because of this unfavourable situation that I cannot wholeheartedly recommend the shop -- at least not their in-store purchase that is sorely lacking.
Overall rating: 7/10
Summary: there is room for improvement, and I'm still looking for my sweet spots, but overall okay.
I sat on this for a week now, about 10 hours daily. I no longer feel lower backaches compared to when I had only the plastic chair, but now I'm still struggling with a bit of shoulder ache, also trying to self-correct on my bad sitting posture. No ergonomic chair will help if your posture is wrong.
Update: I learned that one major reason to my shoulder ache is because of my work desk - it's too tall for me. I work around by maxing out seat and armrest heights to level my arms with the tabletop, but I end up straining my shoulders for that, and I have to rest my legs on a footrest.
It has many adjustable parts so it took me a while to get the adjustments right but that is a good problem to have

I love the legrest, the minor topup was totally worth it.
Wide seat allows me to be flexible and fold my legs up if I want to (not recommended for ergonomics though).
-1 Limited armrest adjustment: as I only occupy 60-70% of the chair, the armrests are too far apart for me. They are a bit awkward for me to rest both arms on.
-1 Armrest discomfort: plastic made armrests (I presume for durability reason) are a bitch to rest your elbows on. Boy they hurt when I rest on them for prolonged period. It does not help that my old cheap desk is not 100% fit to the chair and myself, so I cannot have a 90 degree ergonomic elbow posture. Will need to DIY wrap them with something softer, but I guess they will stick out like sore thumbs,... if you care about looks.
-0.5 headrest is very, very hard to adjust. I'm still looking for a good spot for me but I feel the need to adjust it every time I alternate between lounging and working. At least after adjusting, I can feel my head and neck are rested.
-0.5 Can't lie on your back further than 100~110 degrees. Wanna lie further back when I'm off work... but I can't feel lazy enough lol.
Other comparisons:
Benel Q-MeshThis was my office chair, I think... they're more than 8 years old so it's a bit hard to find an older model. I used to think they were great, until I went back just last Friday to sit on them again. The lumbar support was horrendous as it the depth is not adjustable. I never realised it was not suitable for me before this because I always had my plushie to cushion my back (but due to pandemic, I took it home). Also, only the back is mesh, but it was not a problem for me at the office because it's air conditioned. All in all it is simply inferior to Sihoo M57 is terms of adjustability, but I guess the durability is definitely proven, having lasted so long in my company office lol.
IKEA MatchspelI tested it at their outlet, which was also air conditioned, but I reckon it will not be a nice sit for me at home due to its leather seat. Otherwise, I think the mesh is comparably softer(?).
Headrest was a little awkward and not adjustable enough. Could've been a decent choice if they offered a full mesh version. On other note with IKEA chairs, they are generally not very adjustable, so it's easy to find them incompatible, which turned out to be the case for Markus on me.
This post has been edited by Takudan: Jan 4 2022, 08:22 PM