Zero Rust dries rockhard and lasts for a very long time on my truck. In fact, where I put it on a couple of years ago still looks new. I put it on my bumperbrackets, for instance, and it is impossible to scratch with your fingernail or even most tools.
It is easy to spray, acts and thins like paint (of all things).
I have never tried POR15 but find no reason to change.
