that's an official ROM. what I meant by custom Roms are the ones the redmi has. such as stock android. vivo funtouch os. vibe ui. and stuff. however the 1s is notably faster. but I've seen what kitkat can do for mtk processors.
True, can't agree more. I would really appreciate if those who have the battery problem share their thoughts and observations here, by confirming if you face battery issues. :http://en.miui.com/thread-25507-1-1.html
I opened a bug report on the official miui forum. The more confirmations of battery issue being report, the more the miui team will concentrate on it.