Please MOVE UNDO BUTTON to a more thumb friendly location, as it is impossible to press undo when holding the iPad with one hand. It should be above the other buttons on the left hand side of the screen.
Undo button is the button I use by far the most because of the pen accidentally touching the screen and having it most convenient makes perfect sense. Right now it feels like an afterthought down in the corner.
Otherwise great app. Totally overpriced for hobbyists IMO, but given all the similar feedback I’m guessing you will come up with some middle ground option soon.