QR. For remedial work they have their place BUT only in experienced hands and only for very short periods. IME they are very rarely used well and put a horse into an incorrect outline plus they weight the forehand even more than nature does.
IMO the only way to get a horse to put his hinds further under him is to shift the weight backwards by lifting the shoulders, under saddle or in hand, and this cannot possibly happen in the pessoa. Almost all these 'gadgets' try and push the hind end under and forwards yet nothing encourages the vital lift at the front.
I do own a pessoa and do use it very occasionally but only for very specific reasons and only for a few minutes.
I think their success depends entirely on the individual horse.
We use them when breaking the yougsters because it teaches them to go sweetly and in a rounded basic shape.
The horses they don't work on are those already on their forehand or who tend to go behind the vertical. The pessoa seems to make this worse.
We prefer to use a roller with driving terrets sticking up at three levels and two long lunge reins. These can be used round the quarters or straight back over the roller to your hands.
You have total refinement, you can place the horse's body exactly how you want it and with practice can change the rein at trot on figures of eight.
We use a combination of both the pessoa and the long reining to achieve a balanced calm horse before we get on.
as gadgets go, this is probably the best of the lot.
I have used a pessoa but don't like it. In the end I always go back to the simplest of training aids - the chambon. I helps enormously with young unformed horses to develop the correct neck muscles (on top not underneath the neck) & the back muscles. I like it because there is never any "fixing" of the head, never any back-pull on the mouth, only pressure behind the pole which encourages the horse to drop & stretch it's neck & head. However, it is possible that over-use with horses that are heavy in front could put the horse too much on the forehand. After the initial use of one lounge line to get the horse going round & away from me in circles, I use 2 lounge lines, still on a circle. I find I can control both the forehand & quarters so much better, avoiding evasions such as falling in/out, turning in or turning right around on the "stiff" rein. I only ever use side reins (very loosely) to prevent the horse eating (I only have a field to lunge in) & not as a training aid. I feel that they can encourage a horse to go behind the vertical & lean on the hands. Incidentally, I use the chambon & lunge with a bitless bridle as that is what I ride in by preference. I am retraining a young TB at present who is extremely sensitive to all tack/aids & is inclined to panic so a bitless bridle is especially useful in his case.
I'm not a big fan of them, they have their uses in the right hands but when used incorrectly can cause a lot of damage.
I've known horses damage their backs through bucking with them on, and I spent some time working for an international dressage rider, who used a pessoa on a few horses, but only on the lowest setting and only in walk and trot, for the same reason.