Mi Power Bank 2i 20000mAh is overall a very good power bank. I am using it for quite a few days.
It supports two-way quick charge which means you can charge the power bank and at the same time you can charge your phone from the power bank. I really like this feature. I have an around 3000 mAh battery phone which I can charge via this for about 5 times. It supports fast charging upto 18W. It charges itself also with maximum input of 18W. It also has a low power mode feature which enables you to charge small devices like fitness trackers, bluetooth earphones.etc which consumes less power input.