I've used All Metal, bondo and solder. I don't have a problem with any of them. All Metal will get rock hard and you need to get it filed and sanded right away before it gets completely hard. With solder, the metal should be straightened out (morso than using bondo) so "minimal" solder is used. You do not want it too thick. Bondo is the easiest to use and is a little more flexible, but, I agree with Tiny about the thickness. 1/4" is too thick for anything.