@PollyRoulllson Correct - the rings themselves don't tighten, they are only there to hold the pieces of the headcollar together.
If, however, your dog moves his head quickly and tugs into the dogmatic while there is resistance (you holding the lead), or - worse - the handler jerks on the lead, then lateral movement will cause those rings to pinch in the same way that the rings or side pieces on a horse's bit will.
I'm sure it's not designed to do that but nevertheless it does and I've seen (and heard!) it happen with several dogs of different breeds and sizes.
As I said, what fits and suits one dog cannot possibly suit and fit all dogs. I'm not advocating any particular type or brand but just saying that what is comfortable for the dog is most important.
The Canny Collar has a plastic clip under the chin which can dig in and rub when the noseband is in use and the flat collar part of it sits very high on the neck right behind the dog's ears, which is also frowned upon by some but it can be very useful for big strong dogs in lead training.
The Halti twists and rides up and is fiddly to deal with quicky if your dog switches sides, since your lead must be in the right place to use it correctly without it twisting further. It's probably one of the more awkward types to use, particularly for beginner (or rough!) handlers but because it's everywhere you see a lot of twisty-necked squinting dogs.
And again, anything can be used aversively or become aversive depending on how and by whom it is used and in what situation.