The one I saw used on my RZ tank was electric, the stud was zapped on in half a second. The tank had just come off the bike and still had a small amount of gas in it. The guy said it was no problem, but I stood back a safe distance anyway. Of course they are expensive to buy, if the bodyshop has one the charge is minimal, five bucks in my case. The dent was about six inches across and an inch deep, with me pulling on the stud and a friend tapping around the edges of the dent it was 95% gone. Some Bondo and sanding and you can't tell the dent was there. Now I hope I don't replace the dent with another one!