The tool looks to be an advantage or convenience for cutting copes. I
would also recommend, whether either using the tool or cutting by
hand, to do as Norm suggests: After your 45° miter cut, mark/
highlight the outer face (profile) edge with a pencil, so that you can
more easily see and follow the proper line of cut. For those of us
with failing close-up eyesight, this highlighting mark is helpful.

Sonny