Experienced trainers disagree with me on this point so I decided to do a simple experiment, to prove that I was right. I wrapped one of these collars around my arm and got someone to pull gently on it. It hurt. Then I asked the same person to pull hard. It hurt a lot.
I really feel that the best advice I can give about dog training is that you should always be kind to your dog and never scold it unnecessarily during training as it might not have understood exactly what you wanted it to do.