I've been thinking about one of these ages.
I suppose as a very quick clean you could always foam lance the car and then use a water filter afterwards to ensure no spotting. Probably best in winter but as a good quick clean I think its a good idea.
One of the guys over on Tyresmoke bought one from D'Aqua with american resin in it and has never looked back. The important thing to look for is the quality of the resin. The yanks always tend to come out on tops as ever ;-)
Any comments guys?