With code editing, I keep the pen between the thumb and the palm while touch typing, which works because the pen is very light, so you can almost forget that you are still holding it.

This allows much faster transitions between typing and pointing than with a mouse.

I have not tried a vertical mouse, but I agree that it is likely to solve most of the comfort problems caused by a classic mouse.

Nevertheless, there is no chance for it to be as fast and accurate as a pen. With the pen I can point to any place on the screen pretty much instantaneously and using a negligible muscular force, due to its lightness.