I've tried a few brushes that just push the gunk around, but this nylon head actually scours the hard-to-reach nooks and crannies of my water bottle. The bristles are stiff enough to scrub without scratching.
William★★★★☆
The nylon bristles get into the curve at the bottom of my water bottle way better than my old sponge brush did. Only thing is it's a bit stiff at first, but it loosened up after a few washes.
Isabella★★★★☆
The nylon head scrubs the bottom corners of my tall water bottle way better than my old sponge brush did. Only nitpick is the handle gets slippery when soapy, but it still gets the job done.