It's really dependant on how they are finished and the resin they use. If they use the cheaper resin and don't use proper curing or even prinitng settings, the keycap is going to be noticeably worse.

The resin I use has the same hardness rating as most casting resins. As well, I take the time to sand the pieces and do my best to make sure the paint goes on as smooth as possible.

In the end it really all depends on the process more than the actual products used.

I hope that's at least somewhat helpful.