I've been using this phone from 3 months and I've faced some lagging issues even the RAM was clear.The phone is good for only normal usage.It comes with 'Android One'as all the 'Mi A'series phones.The UI is pretty good only if you don't use your phone much.But if you switch from other UI to this one it will be difficult for you.As stock android offers a very limited in built apps as compared to other UIs.It lacks native screen recording, compass, a native call recorder etc.It offers whole screen screenshot without customising it whereas other phones provide a variety of screenshot options.But the multitasking is really good and the other services of google run well as it comes with Android9.
Gaming experience is preety good but afterwards it gets lagging, the phone gets heated for only 1-2 minutes, after that it becomes normal.The battery performance is also very good as it comes with 4030mah battery and supports quick charging.The cameras clicks awesome photos with its triple camera setup.The portrait mode is not that good but is still acceptable.The front camera has no comparison with its 32mp and it also offers 4k video recording.It has a super amoled screen which provides a super viewing experience.The overall performance is very smooth until you start doing very work but it still manages it.The SD665 does it work really well.The indisplay fingerprint scanner is fast and reliable.It also has all types of sensors along with IR blaster.
In my view the phone is budget friendly and offers pretty good features.But if you are switching on it after using other UIs then it will be difficult to adapt it.