The device is small enough that you can keep it in your pocket. It’s hardly large enough to prevent you from charging and using your phone at the same time as well. Worst case, you can hook up your device and let it charge in your hand bag or backpack.
Unfortunately, these things haven’t gone into development yet, but here’s hoping that they make the jump to consumer electronics one day.  I assume there’s a demand for these, so I’d be on the lookout for them hitting stores at some point.
Be sure to also check out this other cool charger, the XD Design Solar Window Charger by XD Modo. Also, be sure to scope out the Aurelia LED Lamp by Qis Design.