I'm not sure I really understand your idea.. what is the point of having slides within slides?

I do like the idea of being able to customize a "playlist" of slides to flip through and study, which it seems like this app can do.

I also like the idea of being able to study using your phone. Think about if you're on the bus/train, in a boring lecture, etc.. and want to better use your time. Bust out the phone and do a little studying.

One other thing to consider, not all classes can be studied for using flashcards. I don't see this as a problem really since most can.