I'm on the matrix server of a research group that self-hosts matrix (Synapse). It has been quite low maintenance, has around 15 users, and as it's on a server

I'm on the matrix server of a research group that self-hosts matrix (Synapse). It has been quite low maintenance, has around 15 users, and as it's on a server that's already running the group's website, the running costs other than the time maintaining it are minimal. As an additional advantage over per-user-priced options, it has very low barriers for loose collaborations. There's no reason to fret over giving someone an account if they might ever use it. And if someone already has a matrix account elsewhere, federation means we can just add their accounts to our rooms.