The UI for the New Block with the yellow line to show the final position, and the plus icon to add it is interesting, but at the moment, far too finicky.
It requires a level of mouse precision and time consumption that is awkward at best. Perhaps there is some possibility to highlight larger areas, and make the clickable area for the selection far more obvious and easy to click. What do people think?
Ultimately, though, it would be great if this could all be done more easily with the keyboard.