I have a GB436" frame with dedicated magura mounts (4 bolt). Would I gain anything using a brake booster or would it be overkill?
Not sure about unicycles, but I just got my mod and when I apply the maggies, each of the stays moves out a half inch. Worth it in that application. Probably so in unicycles.
No need with a GB4 frame. You don’t put enough force on the brake to really flex the frame. I don’t have a booster on my GB4 36" uni, and I see absolutely no reason to put one on.
The boosters are handy for the other style of Magura brake mount. The single post style brake mount (as used for v-brakes). With that type of mount the booster is nice because it keeps the brake pads from pivoting in towards the wheel. The booster can also be useful if you have a particularly wiggly frame that flexes a lot when the brake is applied. The GB4 frames are not wiggly and don’t need a booster.
Not to mention you’d have to find some longer bolts. Further, the heads are recessed, so a booster isn’t going to sit on the mount very well.
Obviously I agree with JC. 