The main difference between a check chain and a prong collar and a head halter and a front clip harness is that the check chains and prong collars are designed to inflict pain and hurt. The head halter (which I do not recommend) and the front clip harness are not. The dog might still find the tool aversive but lets just leave this topic for another time.
If a trainer uses check chains, prong collars or shock collars he is prepared to inflict pain, intimidate and bully the dog. That is these trainers choice and there is, unfortunately, no law against it.
However, what is important is that the client knows that the trainer is prepared to hurt. It is called informed consent and part of ethical behaviour in business.
Interestingly enough on the websites and facebook pages you neve see these trainers check, yell, hang or otherwise using aversive methods. All you see is when they use positive reinforcement. I find that rather strange. If you advocate those methods show the client exactly how that looks so they know what is going to happen and can make an informed choice.
For more information you might find this interesting. http://petprofessionalguild.com/callforchangetrainingequipment