I like it, nice and simple. I tried it with Astropad so I can markup from an iPad and that works pretty well.

couple of things:

when screen annotation off, two finger scrolling gestures don't work (though scrolling with arrow keys for example still does). Not sure if that was intentional

It would be nicer if the erase tool was a real eraser, and not just a way to clear the full screen (since turning off annotations already does that anyway