Session is very much not a clone of Signal. They forked it way back and the entire back end and front end are different. Session uses the lokinet behind the scenes which stores messages encrypted and routes traffic. Session isn’t completely decentralized to my knowledge as its a work in progress but for now it is harder to block or censor compared to signal.
Even if you have your doubts, its been audited and found to be reasonably secure so it shouldn’t be a security risk. I still don’t use it due to its lack of invites but if they add stable calls I might just switch. For now I use it to send data between my devices.