Used correctly prongs are fantastic tools. Used incorrectly they can be abusive. Important thing to remember when using them is to be tactful. Proper use of one is really something best coached 1 on 1. You cant really learn by reading about it and to a certain extent most probably couldnt learn to use them well by watching someone in a video. It has to be felt.
Use of them also varies dog to dog and situation to situation. It can be a little tricky.