I compared 4 different solar panels (buying and returning). The Solio Classic, SolarMio Pro, and the two smallest Goal Zero models. This one wins for the following reasons:
-only 5.5 oz, one of the lightest
-standard USB output, no proprietary cables needed
-good performance in moderate and high light. None that I tested perform at all in low light, but I'm guessing that's normal despite what companies advertise.
Only negative, no internal battery. So charging an iPhone or other device will only work if the sun is consistent and direct. If you're hiking with this on your pack, you might wise to get a battery pack. I compared those too and the Anker Astro was the best performance/weight that I saw out there.