Hex wrenches, particularly small ones, do wear out over time and use. The edges of the hex round off and you either have to cut them off shorter* or replace them. Even good quality hex wrenches aren't a long term investment. Craftsman tools are generally very good quality and very reasonably priced.

* Do not attempt to cut a hex wrench, even a cheap one, with a hacksaw as they are much too hard. Use a Dremel tool with a cut-off wheel and feed the wrench slowly with frequent dips in water to keep the steel cool and protect the temper.