I have a RAVPower too, but the big SD card version. They aren't pretty, but they get the job done. I haven't had it die on me in the middle of something yet. I use it to watch videos via Infuse, and use Documents by Readdle to look through it and pull stuff out. GoodReader can connect to it too.
I prefer the ability to be able to switch between cards because it makes it easier to add/remove data without being dependent on the USB wire. The biggest issue would be if the battery stopped working, but then you could just have it sitting in a socket.
The actual connection interface isn't that great either, but it's a small thing. It will do a passthrough to the wifi network so you can use the internet as normal while hooked up to it too.