I have no idea about their quality but some day I will take the plunge and buy.
Got Redmi Note 3 Pro a while back from China.
Came unlocked (+) but rom was adware probably installed by seller (-) - installed CM immediately and it was trivial (it did require a PC and a few CLI commands so for end users this might not be as trivial).
So about the phone - the reason I got it is because it seemed like a smartphone that had everything I needed (browsing/4g/streaming) at a price point where I wouldn't care if I lost it or it broke down (~150€ with VAT after imports). The screen is great, touch accuracy is very good which was my main problem with cheap chinese phones before. Battery life is OK, lasts me a day with 4G and WiFi on and a few hours of active use. One problem that was specific to my device I guess is that the notification LED is stuck in red - it blinks in other colors when I get notifications, etc. but it's always red (and this was before I installed CM). Maybe pulling the battery out and returning it would fix it but that seemed involved and I don't care enough it doesn't bother me anymore. Camera is mediocre, it will snap pictures when I need to share something practical (like sending a picture of a document that arrived or a package or stuff like that), but it's not something I would for taking photos - but I don't do that anyway so it doesn't matter to me. Fingerprint sensor works fine. It doesn't look cheap. Overall great value for money, unless you need a phone for taking photos I don't see why you would pay more for an android phone as an average user.
MIUI has options to set all notifications, calls and messaging. So any app that doesn't have own color settings blinks in the color of the default set. For apps that don't have LED notifications (I'm looking at you Instagram, is it really so hard in 2017) I use Light Manager app.
Battery is awesome, can last of a couple of days of normal use(for me)
What I dont really like is the UI, I love the stock android(used to have 2 nexus 4). The UI forces to do stuff in a way I dont like.
The performance is fine... but I got some freezes now and then that I dont expect from a phone with its specs.
And the materials are ok... it has fallen to the ground several times and the glass has broken in a couple of places, but still work... my both nexus 4 got similar broken glasses and both touchscreens stopped working, so in that aspect its better.
All in all, for the low price I find it great.
Head-fi: http://www.head-fi.org/t/786589/xiaomi-hybrid-iem-thread-pis...
Xiaomi: http://www.mi.com/quantie/
MIUI is pretty good too. I'm not an Android user though, so my experience is somewhat limited with regards to what else is out there.
Also their laptop is a really polished product.
Xiaomi phones have the same problem as all Chinese phones: If you can't put Cyanogen mod on it, it is close to useless.
They even fixed the shitty non existant backup/restore situation on Android, hence why Titanium Backup&Restore is the best selling paid app for years. Built in solution backups apps with data (also overrides backup permission set in manifest) and all system settings. You can run it periodically, save in desired storage location, locally or in MI Cloud. After I had to reflash cousins phone which had a vendor MIUI installed, the restore did everything and was almost a 1:1 copy.
Not to mention updates, my budget 135€ device has January 2017 Android security update and is updated weekly.
It has it's own funny things though, like expanding notifications with two fingers only and a bit fiddling to allow apps to run in background and receive notifications, but this whitelisting isn't anything different that other Android vendors have done to save battery.
I found the software a bit frustrating but I can tell you the build quality was the best I've experienced in a phone. Mind you, all my phones have been sub £200.