I like these powerbanks not for what people think they can do with them and that is let them go to nothing and they will charge to 100% as they dont work like that. You charge them fully and after they are fully charged and you go camping or picnic whatever.
You just lay it out and it will stay topped up after you have charged what ever it is you are charging. Just the fact if you where ever going to be in a potision, lets says you are hiking and yur phone ran out. Even if these solar chargers take a while to get 10% on your pnone its better than none to make the call you need.
So they will not fully charge in 12 hours of sun but they are more like emegancy backup for your powerbank you should fully charge anyway before leaving the home.
I think this one is stuff and rugged and im sure they will get them to charge faster in future and thats the only reason for the 4 stars. They also have torch built in which is great for camping or genral torch around the home if you ever need one.