Not to be outdone by Nina, Gustavo also has a pretty chill script for comparing character sets across two UFOs. It appears that Commercial Type has one as well. There are multiple people writing the same scripts. Does that seem wasteful to you? At any rate, here is Gustavo’s.
A very simple little guy to check one character set against another. It lets you select a master UFO, and then the UFO you would like to compare, then it prints a list of the missing glyphs in the compared UFO, and marks those glyphs red in the master UFO.