I've actually tried these types of brakes on two different guns. The first was a rather strange looking Ruger MKII target .223 rifle, which had been converted to a 10rd fixed mag and had one of the JP brakes on it. The gun didn't move when fired, but was LOUD! I would compare it to my 11.5" AR15, which is very loud. I couldn't imagine shooting either without protection.
The second was on a Armalite single shot .50 BMG, which uses a similar type brake. It makes recoil bearable, but is still loud. However, anytime you're launching a 650gr bullet at 2700+ fps, then your last concern is a little noise!
One thing you need to consider is these brakes (by design) push a lot of gas perpindicular to the shooter. This is of great concern if you are shooting at a public range, which may have benches fairly close to one another. The .50 we were shooting cleared the top of the bench next to of, and pretty much relocated the next guys targets, empty boxes, and soft sided gun case to the floor.
Ooops!