Simplex shy away from User ID, which means you are giving up something in exchange (notably no message encrypted-at-rest in their server): then the government can access the message contents from Simplex server.
It says so on their website:
"Only client devices store user profiles, contacts and groups; the messages are sent with 2-layer End-to-end encryption."
What it does NOT say is that message content remains encrypted on their server like Signal does.
It is like time, money, resource: pick only two. But in secured communication, that would be personal anonymity, personal privacy, and personal security: only can pick two.