I tend to steer clear of them because most have the pressure turned way up so they can "get the car clean" without taking forever or needing alot of scrubbing or anything... I don't like this, I just like the idea of the under-carriage cleaning to get crap out that I can't get to with a regular sprayer. I actually do all my car cleaning at the house in the driveway, softer water and I know my brush is clean. but if needed I will do what I must to keep my car from smelling like **** lol