I can't speak specifically about this pump but this is my opinion based on experience with similar products.
It's usually difficult to get an accurate read on how much charge is left in these self contained USB - Li-Ion devices and few use high quality batteries. Just another thing to fail when you need it most. If you use this product, I'd also carry a small compact hand pump as backup.
Personally, I prefer a Co2 inflator with a hand pump backup. Not much to fail with either and you don't have to worry about recharging. Yes, the Co2 cartridges cost money but how many do you actually use?