Meh, I use it. I'll take it over Discord or Telegram any day. But I don't use it for anything that may be sensitive or anything involving IRL people.
It's leaky. I remember all media were uploaded unencrypted and available over https, I don't know if it is still like that. Lots and lots of metadata out in the open. To be searchable you have to give your phone number to a centralized service. The protocol is overly complex, all messages live on all servers of everyone involved in the conversation, lots of duplication, but ActivityPub is like that too and we are on Lemmy...
If I set my own stuff up, I prefer XMPP, and increasingly Simplex. If some project uses matrix, I have an account and will talk to them there.
Overall I'm not a fan, but I don't outright hate it.
No, to be searchable by your friends you have to attach your matrix ID to your phone number and upload it to an identity server, which anyone can run of course but which is useless unless its the new vector identity server. It's a central database of verified matrix IDs.
Yeah, you don't have to. But to be able to easily prove you are who you are to IRL people you will. And the decision tells you something about the product and protocol design.
what? no you dont and the founders have said they dont like them at all since they go against the core of matrix but they make alot of sense in businesses for an internal chat app