I heard some of my mates complained about 4-bolt boosters don't make such a big difference in braking power like 2-bolt ones. Also, it depends on a frame, if it's stiff or not. My HS-33 on the rear used to unclamp the frame too much so I had to obtain one of 4-b boosters from a local Russian manufacturer. Somehow, it's way better now, but since not perfect. People say it's better to try different boosters out before buying one. Mostly, people use boosters to protect magura's hose from damaging, if they have a decent frame, too. This is my setup and it's running pretty decent actually.