If you want a sort of 101 on the Mi Fit band then please check out my earlier post that shows you how to set one up from scratch.
The new version of the Mi Fit App came with some important feature updates that give us hints that Xiaomi have ambitions for extending the Mi range and the over-all offering.
After an earlier app update I'd learnt that there are now a Mi Smart Scales available. These scales aren't officially for sale in the UK. Those that are (check out Amazon), are currently pretty expensive. When I looked into them I learnt that the scales pair with your phone rather than the Mi Fit Band which is poo, but they do what you expect: they keep a track of your weight. I like the idea. One for the future I reckon.
The most recent update of the iPhone Mi Fit app brought us the ability to record weight manually without the need for the scales as you can see in the above picture. So I guess you can try before you buy.