I have had 6 Carwell spraying over the years on 3 different cars and the tech spraying really makes a difference. Sometimes it was a great job, and others I was happy I bought a few cans extra to touch up where they easily missed. The only thing I though of if it doesn't stay on painted and glass surfaces, and a new car should be rust free allowing the penetrating oil to go where? If I was keeping a vehicle over 10 years, I would get the spray after the 3rd year which by then would have some exposed metal in which to bond to. Then again, the warranty from Carwell would be nullified because I waited 3 years to do it.
I keep my vehicles a long time and I'm sure the warranty would have many fine print details I don't want to be bothered with haggling about if I had to use it, but that's just me. Doing it from brand new would almost guarantee a rust free vehicle for as long as you own it. My vehicles are a greasy, dirty oily mess underneath with hardly any rust and I love it!