I like grackles or figure 8 nosebands. They do what a normal flash noseband do except the restrict the jaw from ‘crossing’ which is a way horses avoid the bit. That’s their Main use- to stop jaw crossing. A lot of people use it because they think it’s ‘fancy’ or ‘pretty looking’. And that’s when it can be misused within the sport cause people don’t know how it’s meant to be fitted into a horses face etc. But minus that I quite like them when used properly.
Grackle nosebands are the most strict nosebands, it puts pression on everywhere on the horse's face. It avoids the horse to open the mouth and blocks his jaw mobility. It can be good to spread the pressure but you can't put it on every horse (young horses usually don't support it).
It is also the most difficult to adjust (it has to be in the middle, not too much at right/left or up/down in order not to bother the horse's breathing).
However, it can help the horse not to put his tongue over the snaffle. For every nosebands, you need to adjust it well (not too tight) in order not to harm the horse.
Finally, you have to choose your noseband depending on your horse's morphology.