The charge speed depends on the output current (1A, 1.5A, 2.4A.) The higher the A, the faster the charge. A larger mAh won’t charge your device faster, but a larger A will. If the 2200 mAh and 4000 mAh power bank both have an output of 1A, the time it’ll take to charge your device is the same.
Power banks work with all brands and models— Android, Apple, whatever.
Yes, most of our power banks can be charged and charge other mobile devices at the same time. It varies with different product models and depends on how many outputs the power bank has.