Phone number privacy and usernames are now rolling out to everyone using Signal version 7.0! Update your app to take advantage of these new features 🎇
https://signal.org/blog/phone-number-privacy-usernames/
You'd share a username, which is way different if you ask me. I don't mind sharing my username, Kusimulkku, here but I wouldn't want to share my phone number and real name.
If you use the username to get into contact then your phone number isn't visible to them iirc. Same other way around, your username isn't visible to people you've got into contact with a phone number. So no need to worry about your phone number leaking or your friends and family seeing that you also go by "MonsterCock2000" or something.
What I mean is that the username only serves to connect two users. But the profile they then see of each other is their standard Signal profile, with whatever name and other info it contains.
In addition to what the other user said, usernames are both optional and easy to change in order to prevent spammers from finding you. Plus, they can only make so many accounts themselves, with the phone number limitation in tow.
Matrix isn’t private at all. All metadata is shared+stored by both your server and mine (no sealed sender). Encryption is worse (no double-ratchet) and there’s no guarantee of encryption at all (some clients don’t even offer it). It’s also a lot harder to get set up and IMO the clients are much worse.
That was exactly my first thought. Might be something for various underground groups, but the normal use case seems to be just regular communication among friends & family.