I've heard George Iny from APA.ca say that when he talks to body shops, the cars they *don't* see are ones treated with Krown. I've heard Doug Bethune (
http://www.cbc.ca/maritimenoon/phone-in-regulars.html) say that when he does the same, he hears they don't see Rust Checked cars.
I went with Rust Check because they were closer and I know/trust the shop manager. The tech who applied it is trained how, not just some guy spraying oil. It took 13 years to run my Acura EL into the ground, and rust was a big part of "the end". I plan for it to take longer for my FR-S.