I hate these things like the effing plague, but I may be forced to use them soon as well, since there is basically NO WAY to self hand wash this car at my present locale. (NOT the one in my avatar.)
The closest hand wash is about 10 miles away, and they want $50.00 for only a hand exterior wash, with nothing else included, and I doubt that they do a very good job even for that exorbitant price.
Mine has never ONCE been through one of these paint killers in the 6 years I've owned it since new delivery.
What I have been doing, and it is FAR from ideal, is washing it during whatever heavy rains we get, but usually that means an air dry the next day, in the sun, so yeah, serious water spots anyway.