I'd say they're pretty severe concidering how hard/stiff they are (the ones I've seen), the way they move when you take contact and how the nose feels after having ay pressure at all for just a few minutes at the side of the nose where the nerves are placed under the skin.
I also think they're kinda dull/non-clear in the signals to the horse, but of course that depends a lot on how the horse is trained. I don't like them tho.
I'd prefer a hackamore, but not on a horse that doesn't need a curb effect.
I' say, go with the snaffle, or if you want biless, a riding cavesson or some sidepull perhaps.