A muzzle break is great if your gun has alot of recoil or you just don't like recoil. I really don't see how it will improve your accuracy at long distance shooting though. You need to practice that and shoot only within your comfort zone.
Muzzle Breaks do provide a fairly large reduction in recoil which is nice. I have one on my 30-06 even though I didn't really need it but it is a real pleasure to shoot now.