I purchased two of these from eastwood at $19 bucks each. They are kind of tricky with the deformed spot welds, i.e. the ones that are higher on one side then the other. I went through and center punched all spot welds first, then I used a small drill bit and started each hole slightly, last I used the spot weld cutter to do the rest. All those steps aren't probably nescessary but I was waiting on the cutters to come in the mail and it sure seemed to keep the wondering down to a minimum.
Pros - Cuts good and is hard to over drill the hole. Also you don't have to go back and grind down the little plugs left behind by the hole saw type.
Cons- They are short and are hard to get into tight corners with the drill. They say they will cut 300 welds before needing sharpening, I did all the spot welds on one inner fender and seemed to stay sharp but we will have to see. I also used lubercaiting oil to help preserve them. The cost, kind of spendy for a cutter. You have to have them sharpened and can't simply replace the cutting head.
I also purchased some of the hole saw types with the center pin, they should be nice to get into the tight areas but I have yet to get them in the mail.