What you get is a solar charger that can charge 2 AA or AAA batteries, as well as all devices (phones) that can charge of USB. You need to have two batteries in the device for it to charge a phone but past that, it works flawlessly on sunny days and even on overcast ones, on a sunny day it takes about a day to fully charge a pair of 2100mAh batteries, in winter on an overcast day, it took about 4 days.
You are really talking about trickle charging with this type of device, but in a SHTF situation I'd be happy to have one.
I tend to use one of them fairly heavily on the parcel shelf of my car and it's still going strong, with zero issues.