I bought this good-looking around a month ago from amazon, because of the low price and the good specifications it was offering in such a low price, but let me tell you friends the specifications are only good on paper and the phone doesn't work quite that good.
Redmi 4a has a 5-inch HD display ( not FHD display) . It has one microsim slot and a hybrid slot that can hold either a nano-sim or a sd card. It runs on MIUI8 based on Android 6.0 Marshmallow out of the box and recently received an ota update.
It has a 13MP rear and 5MP front f/2.2 lens cameras.
The phone supports 4g VoLTE technology.
Some Pros-
i) It supports many Indian languages. So, it is ideal for old-age people who might want to use phone in hindi or other regional language.
ii) Good Battery life.
iii) The camera has many unique features like burst mode, face recognition etc.
iv) Looks and design are good.
Some Cons-
i) Heats a lot on fairly moderate usage.
ii) High-end games like Asphalt 8 lag a lot ( processor issue, maybe) .
iii) Hybrid sim-slot, so you cant use two sims if you want external storage.
iii) Camera quality is not upto the mark.
Conclusion-
I would recommend against buying this phone, instead go for Redmi 3s which is almost in the same budget range and offers lot more features.
