Here are some perfect illustrations of how I hate to see training ads in horse sale ads, from Dragon Driving. Example 1:
Here we have a sweet looking mare in draw reins. You can see that her head is tucked in beyond what we'd call the vertical- if you draw a straight line down from her ears her nose is further back than it should be. Look at the overall picture this is causing- she looks like she would fall forward given the chance, and her hindlegs are not in the right position to carry her weight or the riders, which is what we are aiming for through schooling. This link has some further explanations of this.
Looking at this shot I would be worrying just how much she has been ridden like this, particularly in draw reins, and what she might have learned from it. To avoid the constant pressure of the bit some horses learn to back right off it and not accept the contact, tucking their noses in and fixing there. It's called going behind the bit/vertical or being overbent and it's a really annoying fault to try and correct!
Example 2, and here's another 'great' use of training aids:
This is a horse that definitely looks capable of working very nicely, with a nice active hindleg, but the fact that again, her head is winched in by the rein attached to her girth, immediately worries me. What does she go like without that assistance? Again, although the angle isn't the best, it appears she is being forced behind the bit (an impression not helped by her rider leaning so far back!). Unfortunately both advert pics show her in the same rein, so it's impossible to get a good idea of how she is without it.
To be fair to the owner, she admits in the blurb that the horse is a bit powerful for her at 5'1, so maybe the reins were introduced to help her feel safer and more able to stop. I only hope the 'dressage guy' who is schooling her is not the guy on her here as you'd like to think he could manage without them!
Overall, I'd rather see a horse going the way it goes without these reins and gadgets than a horse strapped down this way, as that's how I'd be able to assess what i might be able to do with it in future. You can't ride a horse in draw reins in a dressage test, so what's the point of only being able to ride it in them at home?