I can't say my water blade ever caused scratches because I didn't use it long enough to find out (one swipe). What put me off was the horrendous screaching sound, reminding me of fingernails on a black board. I just can't psychologically get over using a product on my paint that "emits" such a noise. Other people seem to have good luck with it. I do use it on my windows, even though I get the same sound.
I use the sheeting method, and now only use MF waffle weave from exceldetail.com One of Patrick's blue waffle weaves will fully dry my Maxima and my wife's small pickup with no streaks or scratches (even have microfiber borders). These waffle weaves have replaced my trusty, quality 100% cotton terry towels.
I used to use a chamois way back when, but have learned that without any nap, they can scratch the paint if a speck of something gets dragged across the surface with it. And I would end up with streaking that would require touching up. Same with the water blades (I'm not doubting other's success with it, just emphasizing the potential hazard if paint isn't spotless). Here in NE Louisiana, there is a lot of dust/sand in the air, so I prefer to error on the side of caution.
Dave