A fluted barrel with a brake would cost about 500 bucks to buy off the shelf.
Then you have to fit the brake, thread and chamber the barrel, and yada yada. So, there's the labor side of it too.
Sounds like you got a hell of a deal to me.
Lop off the threaded portion and refit to your action. It'll shoot just fine if everything is done properly. No reason to think other wise.