You can compete quite well in the light bench and cross-stick matches without a false muzzle. I do and shoot as well as anyone. I use a goodien offhand barrel, drum and nipple and a manton lock assembled by myself. The advantage of a false muzzle for round ball shooting is you can use a tighter ball patch combination. For example I use a .490 ball and .18 telfon patching in a 50 cal barrel. Jim Goodien makes a light bench barrel which uses a .490 ball, 18 or 20 thousands patching in a 48 cal barrel. To get the highest velocity you then should use a sealed ignition otherwise you will be burning out nipples. My low tech gun uses 80 grains of 3f swiss. A false muzzle barrel light bench or cross-stick gun will shoot 120 grains of 3f swiss. The main advantage is the increased velocity which reduces (I think) the effect of wind. The locking collar holds the false muzzle on the rifle while you are loading. It is not necessary. One of the more interesting aspects of shooting a rifle with a false muzzle is the sport of locating the muzzle down range after forgetting to remove it.
Slug guns use a false muzzle to center the slug (bullet) while loading, the same for shutzen shooters. Long range rifles, Whitworth, rigby, Gibbs use a bullet smaller than the lands and don't require a false muzzle. Harry Pope and his contempories used a false muzzle on their cartridge rifles. They didn't trust the breach loaders to align the bullet properly so they loaded their cartridge rifles from the muzzle.
False muzzles are another aspect of the game but they won't make a mediocre shooter a good shooter. They might add 1-2 points to a 200 point aggregate.
Pete