The HSGI ones have plastic moulded sides whereas the WAS ones just have stiff material. I've not had any issues with the WAS ones with re-inserting mags so I don't see it as an issue. One of the big problems I had was wanting a double rifle mag pouch because at the time WAS only did single ones. You can MOLLE them together but it's a MASSIVE ballache. About two weeks after I got the feeling back in my fingertips WAS released double rifle mag pouches. Grrrr.
But yes, the main advantage is price. Don't skimp and buy the Chinese made ones as they really are crap.