I have a couple, but don't use them often. My truck is silver with a metal dust, so you cannot see the grime, but you can feel it. After the bar, it is smooth. I do it maybe every other year or so. One time, I was doing some grinding on something metal and the hot metal dust landed on the truck fender and stuck. After a couple days, the metal started to rust leaving a nasty looking fender. Came right off with the clay bar, where it wouldn't with the car wash. Eventually I will use it on the wife's black car, but the paint is new enough that it is still smooth, and is kept in the garage.
