Does a shock collar hurt the dog & do they work when used correctly?

The only drawback I see to them are the people who dont use them correctly. I used one to train my dog as he overpowered me at 4months. He is the best wellbehaved dog I have ever seen and everyone comments on it. If used correctly they are a great training tool...and no they dont hurt the dog. I put the setting only as high as I can handle and its like getting zaped by an 8volt battery...not anywhere as near as high as running into an electric fence