And god help you if you'd like to add a font. You'll need to read hundreds of pages of mostly out of date documentation. Then track down brusque gatekeepers on IRC and obscure communication channels to plead your case, only to be mocked and told simply, "No." You will be told it's not "the Debian way" and hundreds of pages of more documentation will be thrown at you. Almost certainly someone will quiz you on your knowledge of obscure 90's unix minutia and the writings of Eric S. Raymond. And once you pass that gauntlet your font might be accepted in a few months, at which time it's already way out of date and you start the whole process over again.
then it copies any fonts in them to a per-user directory. I don’t see any real benefit to debian users vs apt pinning (apt pinning supports auto update; fnt does not), but it does support installing to other operating systems, which is nice for those people.