It would be great if I could keep placing the same piece without having to hold the shift key, it would make things a lot quicker. If you could select/place with the left mouse button and clear the selection with the right mouse button perhaps?

Also, I'd like to suggest duplicate should just make the piece you've duplicated your current selection rather than actually duplicating it in place as it would speed up the workflow (as above), and lessen the risk that you leave more than one of the same piece at the same coordinates.