Can't speak for Samsung but I can say for Xiaomi, if you are able to get used to MIUI, you will enjoy the features. Software support for Mi flagship line not too bad, Mi MIX 2S Android Pie beta testing beginning soon. Battery life will vary from model to model but may require changing after the 18 month mark probably? My Mi 5 battery cmi after it just hit 18 months. Quite common for other models from what I read.
If you are dealing with local Xiaomi set, let's just say their service centre standard is indeed "you get what you paid for", leaves a lot to be desired to put it bluntly.
Sent from Xiaomi Mi 5 using GAGT