IMO the idea of a correction is simply to get the dogs attention and really you can do that either with a harness or collar so I can't see the difference personally. Martingales are good collars and the correction shouldn't be harsh at all just a gentle reminder that you are there, if you really need to do it. You should be able to use either a collar or harness if used properly. Just think they show Cavalier King Charles Spaniels on show leashes so if they can train their dogs on collar you can train yours!!! Being able to work your dog with different things isn't a bad idea either, think one day if your harness breaks, you want to be able to rig a collar and leash up and walk your dog back to safety etc....