Coping is superior for inside corners because it's more tolerant of the trim shrinking or swelling with seasonal changes. Tools similar to that are more of a help on outside corners, which have to be mitered and are never square.
Digital protractors certainly exist, but obviously require you to divide the angle in half. The big draw of that gizmo is it does the division for you and can be put directly on the saw. The less you have to measure the better. (It also prevents you from being a bonehead and forgetting that the miter saw is marked off for roofing angles.)
It's also possible to transfer the miter angle directly with overlapping scrap blocks, eliminating the tool entirely. That rapidly gets to be less and less efficient the more outside corners you've got to deal with though. Shaving five minutes off a corner isn't a big deal when you remodel your kitchen, but it's definitely a big deal by the time you get to thirty corners.