I had a Xiaomi Air Purifier 2S for a couple of years now and no issues.
I have tried a few other brands and I would definitely recommend Xiaomi Air Purifiers.
Pros:
Very affordable compared to most other brands
Very effective filtration (verified with Laser Egg Air Quality meter)
Silent operation on low-medium levels, but still effective
Filter seems to last long (1 year for me in Bangkok, YMMV)
Wifi connection, can be controlled via app
Elegant design that blends in with most types of furniture
Small footprint, doesn't use up much space
Relatively precise built-in PM2.5 sensor (verified with Laser Egg)
Cons:
Filters are a bit more expensive than some other brands (it's still one of the cheapest air purifiers to operate)
Auto mode is useless because what it deems acceptable AQI is way too high (it's a shame because the built-in PM2.5 sensor is precise)
The 3/3H model has a bit of an annoying high pitched sound at high levels, no issues with my 4 Lite and 4 Pro model though
Wish the app had a few more functions and Apple HomeKit integration
Other brands I have tried:
- Sharp (can't remember which model): Weaker performance, pricier, annoying negative ion generator
- Smart Air Sqair: Weak performance except on the highest level (loud!), takes up more space, no PM2.5 sensor, no wifi connectivity
PS: I would recommend always buying the international version of Xiaomi devices to avoid any app compatibility issues