Actually, as a AC specialist. Most brands are okay. Parts are made to failed after 3-10 years for new models and most important is the spare parts. The worst brand for parts replacement is KOREAN brand. Avoid if possible.

For those looking for cheap installation R410A gas AC is looking for trouble. The proper ways to install R410A is to :
1) use correct copper tube size (those old house more than 5 years are not recommended) so buyers need to install new hose
2) Need to vacuum the system and this need at least 20-35minutes.
3) Need to charge extra R410A gas if pipe too long. R410A gas now selling at RM400/tank.

If someone quoted you RM 150-180 for new installation, you better avoid. A proper installation needs all above and skipping one of the above will resulted inefficiency in cooling & electricity consumption.

My 2 cents

Copper size depends on how many tons or hp : R410 use thicker copper.
I assume most are mini split unit for home and shop-lot.
1 hp : 1/4" and 3/8"
1.5 hp : 1/4" and 1/2"
When you see ice build up at the vapor line (the smaller tube near compressor) and the indoor fin, meaning not enough gas. Investigate the leaking, 95% due to connector.
Your electricity bill will double/triple if you still continue to ON the A/C unit because compressor will not cut-off.

So, the question is how long the gas could last? The answer is forever but even a perfect flare will not guarantee 100% no leaking.
A good installation could last you more than 10 years of gas, gas will start to leak due to :
1) vibration of compressor, flare connection, liquid nut, rubber inside the nut (start to worn out after > 5-10 years)
2) bad flare, bad connection, etc

My 1 cents

Not cooling could be :
1) Blower (indoor unit) wind not strong/not blowing -->indoor capacitor RM 3 (can diy)
2) Check compressor (outdoor unit), if ice building up at vapor line --->. need to recharge gas (need handyman to repair leaking & charging)
3) Compressor or fan not starting up --> investigate & start checking fan & compressor capacitor (can diy)
4) A/C cool for first few minutes --> Fan problem and/or compressor overheat heating (need handyman)

** if your compressor not blowing hot and strong wind, you have problem with A/C**
To check leaking, use soap mixed with water will do. No need spend extra $.

If leaking via the connector, try tighten the nut. If still leaking, either you call an AC handyman.
No point DIYing if you only have 1 or 2 units, because you need to buy many tools :
-  flaring tools & cutter RM 50-90
- manifolds gauge RM 130
- R410A gas 13kg RM 400 (can use >10 times though)
- vacuum pump RM 250-350
- Clamp meter to check amp draw RM 50 - 200