Very cool -- this is a very ingenious design. Kudos to the guy for thinking outside of the box
I've made a similar DIY unit for larger fender repairs using a very inexpensive AC stick welder. Just use a cheap HF slide hammer dent puller, attach the welder ground clamp as usual to the car body and add a push button switch to the positive side of the circuit. Push the button for a second and the dent puller will spot weld itself to the fender. The slide hammer tip will need to made out of copper -- I machined mine out of a copper pipe fitting. Then use the slide hammer to pull the dent out.
It's basically the same principle as getting your electrode stuck when striking an arc, but in this case getting the slide hammer tip stuck on the fender is the whole idea.
