Some on here have them or have had them. They do work if you like the looks of them.
have my gunsmith here locally turn the eliminator to the dia. of my barrel.
If you're talking about the junction between the barrel and the brake then that's good. If you're talking about the outside diameter of the main part of the brake that wouldn't be good. You'd lose the effect of the BIG brake. If you leave it full diameter make sure your smith indexes it properly or it'll look really goofy listing to port, or starboard.
I've personally never had a JP brake but I have had great luck with the Holland QD types and Kirby and Shawn both make equal or better brakes.;)