My group has been tinkering with matrix but the ecosystem is such a mess that I think we'll be going to xmpp-based solutions, and once the kinks are ironed out, migrating it to i2p
Not to go all conspiracy-nut, but it feels like the net (at least the social spaces) is decaying, and it feels intentional / coordinated.
These are a decent overview
https://forum.hackliberty.org/t/why-we-abandoned-matrix-the-dark-truth-about-user-security-and-safety/224
https://disroot.org/blog/matrix-closure
I don't agree with all of those points, but that's the gist. The metadata issue is becoming a bigger factor. I hope things like katzenpost find massive success...
As for the ecosystem: Element and Synapse are really the only viable implementations. Fluffychat is okay on android but that's about it; most lack features or are using outdated and vulnerable dependencies / are poorly maintained / etc.
But it's not all negatives. One great thing about Matrix is how well they handle multiple devices. It's also been a security weak point, but not too bad and has (relatively) excellent ux (depending on impl...)