I don't use flash nosebands (and their many variants) anymore. The further I travel along my horsemanship journey, the more I wonder why I would bother. See, I see horsemanship as communication, as play, as exploration. How is it fair to go on an adventure when only one party gets a chance to fully communicate?
I've heard a million reasons for using them, but over and over I just realize that these people are afraid of truly communicating with their horse. I know I was - because it meant changing something if I acknowledged what he was trying to say. When your horse gaps his mouth, sure, he's evading pressure. But I want to hear that. I want to let him start that conversation, so we can address why. Are my hands to rough? Do you not like lateral bit motion? Is this the wrong bit? Would you prefer bitless of some sort? If my horse were always wearing a flash, I could never help him along on this adventure.
Look at it like climbing a mountain. I know, cliche, but it works. You can go hand-in-hand, helping each other and noticing the slightest stumble before it escalates. Or you can watch your friend fall, then throw a grappling hook after him, and tell him to deal with it on his own. I, personally, would prefer the first.