I've used this product for years now. I used it as an "undercoat" for my wife's 2010 Jeep Liberty when we bought it new. Every time I do an oil change, I just look around and touch up as needed. Also use it yearly on my 2006 Tundra - again, touching up every time I'm under the truck. Both vehicles still look excellent underneath, even with the salt solution they use on our roads in Maine winters.
The HD Metal protector is a unique product, and I'm not aware of an "over the counter" item at the local parts store that works the same, or is the same consistency. I've also used Fluid Film briefly, but did not care for it.