I used the Birchwood Casey to touch up a gun with a lot of holster rash. It came out pretty good and has held up so far. Warming the metal up is supposed to make a big difference as well as using multiple light coats. I was able to blend it in to the original finish.
i cleaned it up real good initially,used some 0000 steel wool, washed it with alcohol and then started the process. I think it is like most projects of this type, preparation and patience are the keys to getting a decent result