The thing to remember if you're a foldy used to regular bikes is none of these things are light and you won't be carrying one far, and stairs would not be fun at all. The low end of the weight class is 40 (I'm doubtful of the 30 pound claim) and most that fold Dahon-style are 50 or more.

I recommend them for their ability to store small and occasionally stuff in a van, just don't plan on rushing for the train with them.