It'd be good to have details of unicode coverage on this site, i.e how many glyphs in various major blocks are covered (e.g greek, cyrillic, box drawing, mathematical symbols etc).
The problem here is that the information isn’t always available. If the docs don’t mention box drawing characters, or powerline symbols the font may still have them. Also, a lot of sources mention the number of glyphs but not the Unicode ranges that are covered.