put it this way... they don't HELP baby with anything, in fact the position they are in is more likely to hinder a child learning to stand/walk
so... with that in mind the only reason i can see that people have one is to keep child in one place.
soooooo a far better buy would be either one of those static activity table thingies that you strap them into, or a playpen.
we have a babydan playden which is fantastic. once ds is older he can use it with the tent bit, or we can use it to cordon areas off with