Compared to Matrix, or any E2EE chat, this doesn't sound good:

we take your privacy very seriously. And with end-to-end encryption coming to DMs and group chats soon

Compared to Discord, or other established voice chat systems like Mumble, this doesn't sound great either:

We are currently rebuilding the client and the voice server from scratch. The old voice should work in most cases, but it may inexplicably not connect in some scenarios and / or exhibit weird behaviour.

The "app" on Android seems to be just the webapp running in a standalone window.

I'll concede them the OpenSource and self-hosted factors, and it does look like Discord, but it doesn't seem like a suitable replacement for average users... yet. Then again, the ads might push them over.

Guess it's worth to keep an eye on it.