Magnetic Ground Clamps

I,m curious.Does anybody use a magnetic ground clamp when welding patch panels or quarters on their cars and trucks????I,m on a spot tonight where I welded in a patch panel on the front fender on my truck.I thought wouldn,t it be nice to have one.I seen them advertised.Can anybody tell me good, bad or indifferent on their experience using one??????? Or do you use a vise-grips on and edge and then the regular ground clamp??

I have used one it works when i was doing the quarters i just tack welded a bolt on the package tray that way i had a good ground to clamp to that would reach all around the body shell .