I've used Session for some specific use cases and it's worked well, although it's not really been a fork of Signal for the last three years. They started from the same codebase as Signal in 2019, but the team has made it clear that it's deviated significantly since then. It seems like it became a major selling point for them, as they didn't believe Signal's protocol was a good fit for their decentralized environment anymore. They migrated from Signal's encryption protocol and developed their Session Protocol, dropping Perfect Forward Secrecy behind along the way (which SimpleX grants). Relating to identifiers, the main difference between Session and SimpleX is that the IDs are fixed in Session between users you communicate with, while they can be random and require no identifiers in SimpleX to connect in the first place. There's more that differs, including their decentralization and server ecosystem from what I understand. I believe SimpleX provides a structure for more interesting growth, but that's just my humble, unsolicited opinion, and based on what I value I guess 😂. I see it being more interopable and aligned with the goals of nostr. I'm sure the founder of SimpleX (Evgeny) could expand even more on their differences if people wanted to know. Just thought I'd share in case you're interested, here's some links relating to Session's move away from Signal:

Session

The Session Protocol: What’s changing — and why

Session is moving to a purpose-built new encryption protocol: the Session Protocol. Read all about why we’re making the move, and what it means f...

Session

Session Protocol: Technical implementation details

Read up on the technical information behind the new Session Protocol, and our plans for rolling it out.

And here's an Opt Out episode from @Seth For Privacy with Evgeny about SimpleX. Really interesting stuff:

Opt Out Podcast

SimpleX chat and how privacy aligns with the future of computing w/ Evgeny from SimpleX

Heard of SimpleX chat and curious what it’s all about? This episode, we’re sitting down with Evgeny, the founder of SimpleX Chat to talk about ...