I think it would be the same as any other coating; possibly better, dunno. I think most of what we hear about POR-15 and RustBullet is hype. I understand it's better than paint, but after special consideration and reading and re-reading about this stuff I've determined it to be exceptional marketing. Not that it won't do what it say's it will do, but they're not special or magical and they're definitely overpriced.
Like anything else it's all about the prep work. Don't skimp on prepping the metal and your coating will hold up for years. I've got the factory coating under my YJ and it appears to have held up pretty darn well for 15+ years to Illinois' two seasons (construction and winter). It's time for it to be redone and I'll probly go with powerwash, chip, sand, more powerwash, rust convertor, and then truck bed liner. The stuff Rust-oleum's putting out is comparably inexpensive and readily available.