The charge: 7800mAh, it's huge, it's 5 full load of a modern smartphone, on average ...
The size: it is a few millimeters the size of a normal iPod, or iPhone 3 or 4, if you want (it is thicker, in fact). It's really small for such a battery! Usually one is more in sizes 1.5 times higher.
So for me it's the big advantage of this battery.
Another important point is suitable for iPad, tablets and other recent smartphones because it delivers up to 2.4A!
Finally, I will say that it is solid, I slip it into my bag without anything and resistant to minor impacts. A perfect course for this VERY small battery bear !!