Earlier quoted context omitted.
Because matrix (the open source protocol) is federated, you have options: matrix server (for self-hosting), SDKs, bots, libraries, etc. = https://matrix.org/docs/projects/try-matrix-now matrix clients = https://matrix.org/clients/ matrix bridges (to interoperate between matrix and other services like irc, slack, telegram, etc.) = https://matrix.org/bridges/ if you don't want to manage on your own, and simply want to…
How many users does matrix have? I tried it last fall on 2 different servers. (Hosting an own server is not possible on a small root server you can get for 5 EUR/USD a month, it requires signifcant resources.) My experience was a bit disappointing. It seems pretty overloaded already, especially the irc bridge. And we are talking of thousands of users. I'm pretty convinced that with millions signing up it would collap…
What nobody talks about is that when you start to federate this becomes huge issue. One of your users join some old and active room on matrix original instance... it will kill your instance.
So yeah the idea of federation is nice but right now Matrix is no replacement to Signal for personal messaging. Its great for replacing slack and private community servers though. I use it for that a lot.