Im using it right now. so far the only bug I had was, sometimes when I wake the phone from sleep, it causes like a 1-2 second delay till it pops up. then when screen is awake, miui crash report is generated and asking me if I want to submit the report to miui devs. I think this maybe due to some conflict with MIUI 8's battery saver, because right now I have that OFF, and I havent experienced the said bug so far.
currently using MIUI v8 - 6.7.14 Beta (xiaomi.eu)
I still have my battery monitored. will report here after a day or two.
All I can say for now is, charging took shorter than usual maybe due because of reduced heat from the cpu side when idle, causing quick charge 3 to pump more juice.