Wish I'd read about the Anker before I got my Mercury 10. Just took it for my first test run of it in Yosemite over 6 days.
Like that review says, the included battery is pretty week and not worth carrying. I'm probably going to have to pickup a couple small batteries to charge instead on the trail. I have one small lipstick sized one that worked better than the one that came with the panel and was 1/3 the size.
I also had a couple of the loops fail, so I'll have to do some repairs to be able to hang it on my pack. Still checking with the company about a replacement.
The panel itself does charge things fairly well. Even in overcast skies, it got some juice going. I'll still need to carry at least one of my bigger batteries (18000kwh or 10000kwh) for my big trips and won't bother with the panel for shorter trips of 2-3 days (wasn't planning on that anyway).
So for longer trips a solar charger can be useful, IMHO. I'd just use a big battery for 2-3 day trips.