I tell you for many reasons to not buy Xiaomi Mi A1 smartphone, so lets go to these reasons.
This mobile has a hybrid sim slot.
Have a 3080mAh battery but not good performance. That means battery life is very low.
Not have a NFC sensor.
Not support micro USB. ( This mobile have C type USB port) .
Heats up occasionally.
This mobile support quick charging but fast charger not in the box.
No stabilization in camera.
This mobile not good in price, function and build quality with competitors.