there are other brands like that that I haven't used, I don't know about the rustoleum.
my can I used on an 5' tall antenna tripod, then all the rust spots starting on my car, and I've still got about a 1/3 of a can left.
Never used rustoleum but I've used por15 on cars and outdoor stuff and it works great. I'd imagine that since its not new technology a big company did their homework and have a decent product.