I just want to point out that they don't always evade the bit because they are not comfortable. Personally, I love using a flash on one of my horses, it helps so much. Its not like its really tight on them, I put it just as tight as the regular cavasson. About 2 or 3 fingers. My horse in particular likes to lock his jaw & try to run away bc he wants to run. Having a flash prevents him from gaping open his mouth. Yes he can still chew [he eats all the time with it one] yes he can breathe, NO his mouth is NOT tied shut. I would rather have someone put a flash noseband on a horse then a way harsher bit.
Yes some people do abuse the flash, but 'some' people tend to abuse anything & everything.