Some people might be hesitant to use the Water Blade because they'll fear it's edges would trap very small pieces of dirt that could make tiny scratches in the paint. This won't happen as long as you wash all the dirt off the car and your rinse water is clean. Also, you stand far more of a chance scratching the car with a towel or chamois than you do with the Water Blade because towels and chamois, even after they've been washed, hold tiny specks of dirt in their surfaces. The Water Blade's silicone T-bar edge does not trap dirt.
Source:Audi World review"I'm reasonably confident that the silicon rubber is far too soft to harm the finish (unless some grit gets embedded in it) You still need a towel or two (versus a stack) to wipe the small areas that the Water Blade won't get. Is it worth $20? Only if you really hate handling those sopping wet towels."