I have Wiha, Bondhaus, and Craftsmen metric allen T's. I'd rate them in that order.
The Craftsman's are pretty inexpensive when you get them on sale. So cheap I always pick up a few extra sets....
I just took my Craftsman 3/8" metric allen socket set along with a a few other tools back to sears today for replacement. The 5mm and 6mm bits were getting a bit worn. They replaced them without any drama or questions. They didn't ask what was wrong with them, didn't even look at them as near as I could tell! Just went and grabbed replacements off the shelf. I'm sure they would have done the same with the T's.
I think it depends on which store you go to. I hav two Sears about equal distance from me. The first is awful, staffed with know-nothing, do-nothing minimum wage employees, and the other is fantastic with employees who actually seem to kinda like their job, know a bit about the products they are selling, and actually try to help customers!