There are a lot of RimX guys who use or have used Proof pre-fits with good success. You can do a quick search and find a few threads on it. That's mostly the steels barrels.
If you're looking for feedback about their Tikka, Ruger, or CZ carbon fiber pre-fits you might have a harder time. I don't think I've met or heard of anyone using one on the forums. However I'm sure there are a couple floating around.