Bro, Redmi 3s doesn’t have finger print sensor, only 3s prime has it.
3s - 2 GB RAM, 16 GB internal
3s Prime - 3GB RAM, 32 GB internal, Fingerprint Sensor
It’s the best mobile at this price range. Go ahead and buy.
But only one thing you need to take care - Don’t factory reset your mobile after updating MIUI8, otherwise you will face network issues. It is OS bug and will be corrected in next update. So don’t worry.