They're allright if the cars clean beforehand, which kind of defeats the object.

The first and last time i ever used something like this was on my motorbike. I will never use a waterless cleaner ever again.


When you're cleaning you ideally need to remove the dirt without scraping it around the paintwork. This is why snowfoam combined with jetwashing is so good.
It lifts alot of the dirt from the paint before you set at it with a sponge or washmitt.