It was more like a wet mop thing they used. Sorry for giving you the wrong image about the 'brush'. No scratches.
The turbo timers usually crack me up the most when cops are standing there baffled like "how could this idiot leave his car running?!" lol. A few friends and I were walking into a restaurant while this guys 06 STI was on the longest timer ever for his turbo timer (5 minutes? felt like forever...). From the time we walked in the door 2 different waitresses and a hostess all told us we left our car running. It was a pretty loud stage 2 set up. vibrating the front door and all, kind of annoying to be honest.