|It fits loosely over the dogs nose and is clipped to the dogs collar with a Halti-link. Your lead clips to a ring underneath the chin. So, when your dogs pulls, their head is pulled around to the side.
As the nose loop is loose unless the dog is pulling, this may be comfortable for the dog to wear. It is however easy to paw off, and cannot be kept on when your dog is off lead. Stop Pulling Comment: this may cause a problem - once your dog has realized that it can be pawed off, then they may either keep trying to do that, or remember and paw it off one day just when you need it.
You may not need the halt-link once your dog has become used to wearing the Halti, but it is an extra safety precaution, just in case your dog decides to slip it off their nose - you still have the dog attached to your lead via the halti link and the collar.
There are lots of training notes that come with the Halti using the Halti itself to move the dogs head into e.g. a sit, or a down etc. Or to simply use it as a stop pulling aid. Stop Pulling Comment: Why would you need to pull your dog into position when you could guide them with a hand signal?
Behaviourally, it can be used to close your dog's mouth. Stop Pulling Comment: if you are concerned about keeping your dogs mouth closed, then you may be better with a) a muzzle and b) a stop pulling harness.
You can also use a double training lead, instead of a Halti Link. And, then one end connects to the halti, and one to the dogs main collar.