I love that Undo is button mapped. That was one of my biggest gripes on Tiltbrush.
I find that the sensitivity for small clay lines is not granular enough. I have a hard time picking consistently small line at the bottom of the clay scale. If it goes too small it's like "spittle" and it easily goes too high. I wish the selection allowed for more precise selection at the bottom of the scale, perhaps trigger gets less sensitive or left and right move the trigger more slowly.
Having a blast so far. Will keep experimenting.