I was reading through one of my "horse dictionaries" (yes, 'one of'...I own many =P) and I happened to glance at the tack section and noticed that under the explaination of the usage of a flash noseband this is what it said:
"...The flash noseband should also be attached tightly and securely. You should not be able to fit any fingers between the band and your horse. The noseband's purpose is to strap the mouth shut to prevent the horse evading the bit."
That is not what a flash is used for. If you have to strap your horse's mouth shut to prevent him evading the bit, then you need more training than your horse.