I've taken my TWH gelding out in both a snaffle (full cheek) and a curb bit. Nothing wrong with either, but he does seem to prefer the Robart's pinchless TWH bit (which is basically a less expensive version of the Imus bit). He really relaxes in that bit, very soft and responsive. Most of the time he just needs a little cue with the leg and a voice command to do stuff, anyway, so there's not much need for contact with the bit.
Tried the Imus bit years ago. . .bad experience on the whole, not impressed with the quality at all, and will never touch another one of her products with a ten foot pole, but some people seem pleased with her stuff.
I have heard mixed reviews on the various bitless bridles. Most of the videos people I've seen of bitless bridles (meant to show how well the horse goes "bitless") make me less interested. I see resistant horses with tense movement and hollow backs, heads up, etc. They don't look much happier, and they really don't prove the point they're trying to make.
"Parelli horsemanship is just like painting by the numbers. You need absolutely no skill. You just put this color here and this color there, and when you're done, you have ... a mess no one wants." mp