Recently I bought one Xiaomi device – Redmi Note 3 and have been using this device for 1 month. I personally like MiUI due to:
1. Its immense power to customize the phone according to your way of use
2. Faster response
3. Inbuilt Theme App, Wallpapers – So easy to change the styles.
4. You can change the display settings to a level where you can actually change colours and saturation and adjust it manually.
Though this UI is pretty heavily customized and easy to use – I find lack of an app drawer which Xiaomi can consider adding in future releases. And also as an ex-HTC user I used to easily read the whatsapp notifications without opening the application so that the person in the other end does not even know whether you read the message or not. This way you can actually reply to a message if it requires, or ignore it without hurting the other person 🙂