I've bought the Reebok Realflex before.  These are slightly different, as I had the original, and they aren't quite as lightweight, but they allow your foot the flexibility, while offering protection.  As I said, I've bought them before, so I knew what size to buy.  Can't really offer any advice other than trying on Reebok shoes to know what your size is.  I expect to run these shoes just about to death, and probably put 300-400 miles on them, and they will likely hold up very well.  Don't play basketball in them.  I ripped my last pair (after putting about 300 miles on it) trying to stop too fast.  They can't (and shouldn't) handle quick stops as well as bigger shoes.