The battery is powerful because I could charge my iPhone 5S once, and then I was able to bring the battery from 5% to 80% (or ~ 180% in total).
Note that the output is 1A, so if you connect a tablet, charging is long enough.
For a smartphone (iPhone style), the charge is as fast as the original charger (around 1:30 for a full charge starting at 0%)
LEAST:
* Lack of instructions in French, but considering the price and knowledge have on the battery, it is the lesser evil
MOST:
* It is not necessary to turn on the battery charging starts, it starts when you connect a smartphone to the battery.
* I like the system LEDs that indicate recharging immediately available (1 diode 1-25%, 2 diodes 25-50%, 50-75% and 3 LED diodes 4 finally 75-100%)