I've never seen anyone riding in them other than on the lunge, but I must admit I've lead quite a horsey sheltered life in that I've only been to 2 riding schools.
Do you mean that people ride off the lunge in them? If so why? Sorry to be all questions. Doesn't it interfere with the riders feel of the contact and the horses ability to seek the bit.
A couple of weeks ago my instructor was giving me a lesson on Breeze and picked me up once or twice for every now and then having a saggy outside rien. Breeze is still pretty wobbly and snakes about abit and I was finding it difficult to keep an even contact.
Anyway after the lesson Maggie (my instructor) got a thin rope, held her thumbs up in front of her with the rope wrapped around each thumb mimicking the horses mouth and asked me to drive her, using the contact I feel when I'm riding and aids for direction change and halt. I have always felt and been told I had kind hands and was disappointed when she said she felt a drag when walking forward which made my other aids disguised. We swapped places and she drove me, though I could feel her hands I had freedom to go forward her hands felt like helium filled balloons following me, when she gave an aid it was clear, and left me in no doubt about what she was asking, just a gentle tug and was instantly released. She then drove me in the contact I had driven her, I was horrified, the slight drag, which felt slightly restricting (though I had freedom to go forward I felt a bit contained) and though I could feel the aids they weren't as clear and give wasn't as noticable. Luckily Breeze has understood my muddy contact along with my wieght aids I'm glad I also have lessons on an older horse who only gives whats asked when asked correctly.
Riding in side riens must restrict the riders ability to give, especially if the horse has worked well and their reward is to stretch down and relieve tired muscles and chill out. It takes the partnership out of the relationship, instead of asking, educating and encouraging the horse its restricting, demanding and curbing freedom. My interpretation of dressage/schooling is for horse and rider to be partners, communication, willingingness and freedom to move in natural carraige and balance. Maybe I'm missing something, but I can't see the point in riding off the lunge in them.
Lesley