A few suggestions which I think would improve usability, at least for me.
- configurable default units, or last used units for new new designs.
- hide menu pane when gesture/ pen press in design area
- configurable left lower menu, to upper left corner, as this is more accessible when holding the ipad
- keep circle diameter numerical editable when circle has been completed, now it needs to be selected and then edited. Actually applies to all numerical input.
- measurements, and keep measurements visible (or separate layer)
Keep up the good work!