In short, yes, go for it.
Hopefully that case has the right electronics in to prevent discharging when the panel is outputting less than 5V (which it will most of the time unless in direct sunlight, which is few and far between these days).
Might be worth getting a higher voltage panel (what's the input range of the charger? Or does it just say "USB"?) to account for less than ideal conditions.
Else you might have to get a shotkey diode to prevent discharging, but they're very cheap and very simple to wire in series if you own a soldering iron.
Hopefully that case has the right electronics in to prevent discharging when the panel is outputting less than 5V (which it will most of the time unless in direct sunlight, which is few and far between these days).
Might be worth getting a higher voltage panel (what's the input range of the charger? Or does it just say "USB"?) to account for less than ideal conditions.
Else you might have to get a shotkey diode to prevent discharging, but they're very cheap and very simple to wire in series if you own a soldering iron.