I have the Power Messenger bag with 3000mAH. The bag is nice, the battery is nice... the power OUTPUT sucks.
The Micro and Mini USB output is only 800mA COMBINED.
Most phone nowadays, like my 1.5 years old Galaxy Note 1 requires 1A. Heck, my Galaxy S4 Active need 2A (the power that came with the phone has 2A output).
So if you charge the phone on the go, it will take at least twice as long.
The only way to get more than 1A is to connect a USB cable directly to the battery, but it is located INSIDE the bag, near the bottom that it is incredibly difficult to connect.