It seems a little contradictory. First the article says that the purpose of the font is to eliminate the problem of "this glyph isn't in the font" squares being displayed when you're reading something, but then later on it says that you can download different versions of the font containing different subsets of glyphs
. If you download a version that doesn't contain a glyph used in a text you're reading, the result will be precisely the problem that the font claims to be eliminating.