From my personal expereince I saw the extremes of this phone.
Bought in Dec-2015 from Flipcart under the exchange scheme, continuously using this phone for last 7 months with 99% performance and satisfaction.
Sound quality - excellent.
Camera - excellent
multitasking - better
design- Cute
Any hang problem -~ZERO
Very happy with my choice.
But last weeks, the remaining 1% had got a trigger and then I felt like why I bought this phone?
Problem: while using this phone(i guess watching gallery photos), all of the sudden the display was blacked-out. I thought that it could be due to the battery low-level so charged it, tried to restart it. but as the display was not working, I have not realised whether a phone is on or off.
So after trying for 3-4 times, I connected with laptop and then realized that phone is working internally and using PC-suite I can view everything on the phone including SMSes also but calls could not be made.
I took backup(copy-paste of all contacts, songs and other galary stuff and tried to reset the phone thru the PC-suite itself but failed as it expects you to take some official-backup first before resetting. There is no option to say, I dont want this back up but just reset it.
So then the next set trouble started, took phone to the nearest service centre. I must say the worst-service centre ever visited. The folks there(at Gurgaon - Sec-14) were so insensitive that they do not know how to talk/treat customers. Rude and blunt with their tone(typical of HaryAnasultan), opened job-card and just informed me that you may get it after 10 days, and if any further issues, it may take upto 25 days. 5-days over. wait in-progress.
To be continued-1. 13Jul2016 - Its 18 days since my phone is at Service Centre, No update. Now I am assuming, the problem is worsened.
To be continued-2 01-Aug-2015: Its 35 days since my phone is at Service centre. No update . Escalated to grievance.officer@xiaomi.com and service.in@xiaomi.com but no proper update. I have requested for replacement as part is not available(for 1.5-2 years back launched product). Its really painful.