Prong collars are a training tool that functions off a pressure and release system to aid collar pressure re-sensitization. This tool is great for dogs who pull right through a flat collar as they lessen the surface area of pressure when activated. Prong Collars do not "pinch" or "choke" the dog, they simply apply pressure in the same way as someone giving you a light poke on the shoulder.
These tools shouldn't be used without supplemental training as they will lose their effectiveness. The goal is that your dog doesn't need the tool forever and not all dogs need a prong collar. Just like any tool, they are effective and humane when used properly.
Always be sure to consult a professional trainer before using one!
Scrappy enjoying his training session while wearing a prong collar.