Tonight I used the brush on this center cap. I rubbed it hard for about 30 seconds putting a lot more pressure on it than I would ever do during a normal clean. I held it at ever angle possible and there are no scratches. However, I do agree dirt particles trapped in the brush could be a problem.
Thank you for those of you that received the brush and posted your initial reviews. As I've mentioned before, this brush is one of those things we tried out and really liked it. With this brush, you can clean different parts of the rim that you wouldn't be able to do with other brushes/scrubbers pretty quickly and easily.
Please keep in mind that there are several similar looking brushed on the market today. I believe someone mentioned a similar looking brush they've purchased from Griot's. This is not the same brush and is not make out of the same non-abrasive material. Always look for the "Better Than A Brush" tag and purchase from an authorized dealer/distributor.
Since I have significantly different wheels than most, I found the best use for my brush being the inner barrels. The brush is great for this use on my wheels and means I can now clean the entire barrel without removing my wheels. I'm very pleased with it!