Its a question that I've pondered on for ages, and generally speaking its something I think I'd only consider if my car were a very light colour, like white. Because... no matter what you use, essentially you're dragging sharp dirt across your paint because you've not washed off the coarse stuff first. On my car for instance, using jet wash, snow foam and all the right kit, still results over time in slight scratching. If I used a waterless spray only, I can guarantee I'd ruin the paint in no time at all.
On a white car, you can't see the scratches as much, so I'd risk it on that. Personally, for a darker car, I'd never use the stuff because I wouldn't want to risk the paint.
just half an hour later and by not using much pressure it was sparkling - and there are NO scratches. It works by lifting the dirt and holding it in suspension in the water and mitt - I think 
