Just came across this thread and thought I'd respond, even if it's a year old. Better late than never!
I use a Dr Cook bitless bridle for all horses I ride. I'm a trainer.
These horses have all been mishandled by well-intentioned owners with heavy hands.
The bit was way overused, the horses were overbitted (long shanks) for "control" that ended up turning the horses into hardcore resistant and dangerous rides.
They were basically taught to run through the bit and they did. Some of them would raise their heads SO amazingly high just to escape the massive pressure in their mouths.
I decided then that to restart them with a milder bit would be ok, but going with a bitless would be even better.
I was right on all counts with every single horse.
Most of them took the bitless bridle so well, they were licking and chewing the very first ride.
Some of them didn't like it at first...they'd sling their heads, because they found out that no matter how much they tried to evade it like they had evaded the bit (by raising their heads, etc)....they could not evade the bitless.
BUT...once they realized that the bitless did not hurt (someone here said it was severe? really? well, respectfully...that's just not true). I have not been able to use any form of pain with this bitless bridle and this is why all of the horses would come around to liking it.
There was just no pain. Not like there was with a bit (with bad handling of course! not saying bits are bad)
Once the horses who argued with the bitless at first...realized there was a release of pressure if they simply yielded (relaxed), they calmed down and would lick and chew, look soft-eyed and respond to what I asked (turn, stop, head drop, etc).
I can't say enough of this bridle. I feel safer and more in "control" knowing I can't cause pain, but I can communicate clearly...with this bridle, than with a bit.
So...yeah, to anyone who reads this, I can't recommend this bitless enough.
Oh, and yes, of course I have ridden on all kinds of trails with it, so not just in the arena.
p.s. I haven't gone back to using a bit since starting to use this bridle. And all of my clients have seen the difference in their horses...so they have all bought Bitless bridles.
(again, I have nothing against bits when they are used properly, but a bitless is great for novice hands. It's truly forgiving vs a bit.