It seems to me like it’s almost impossible to buy a bridle without a flash attachment any more, especially a dressage bridle. I guess I’m dating myself, because I have a clear memory of when the opposite was true: the flash was a piece of equipment you added if it were needed, but most horses did without. Now it seems like a fashion accessory
In fact, “way back when” we mostly used drop nosebands (which fell out of fashionable favor sometime when the ice age was receding). Apparently they are ugly.
I wouldn’t have a real problem with the flash noseband except for so many people don’t fit it correctly. I think people forget that the idea behind the flash was to help stabilize the jaw and keep the bit from slipping down. You are not supposed to cinch it so tight that it leaves marks on your horse’s muzzle!
Most often I see flash nosebands (and also figure 8 bridles) adjusted so they are too low — when this happens they can interfere with your horse’s breathing.
To adjust them correctly you need to start by having the cavesson adjusted so that the noseband sits 1-2 fingers below your horse’s cheekbone.
Then adjust the flash strap so that is snug but so you can still fit two fingers under the horse’s jaw.
When a flash strap is too low, or cranked too tight, they exert continuous pressure over the sinus area and can even cause nerve damage.
Flash nosebands can be helpful — I’ve used them on occasion when I had a horse that was opening its mouth and bracing against the bit — but they are not a substitute for training. True relaxation and acceptance of the bit cannot be achieved by strapping your horse’s mouth shut; often resistance in the mouth is caused by the rider.
So if you have to use a flash, make sure that’s adjusted in a way that won’t hinder your horse and think about what you want to accomplish by adding it to your bridle.