You can read the github for all the details. SimpleX has always been multi-platformed. I think their protocol is better then the lokinet routing session does. Both have their ups & downs but if security is the main concern then SimpleX is the way to go. But at this current time session does have better performance for now so if you're looking at performance then yeah session.
Discussion
At time i was testing simplex there was no linux package, maybe i can try again. I go over all documentation, it is progressive project, but sometimes less is better than more. I am against many session technicals, but session i can run on all my devices with same account and restore it on any device because i remember my seed, as far as i can remember simplex does not use seed. I can imagine seed and hd key generation + custom salt password for it, it would be secure, with ability to restore and also custom privacy device by device woth same account, but i do not thing that someone would be able to understand what i am talking about.
The desktop app is being developed as we speak. Since it began SimpleX first ran on CLI so for any os you can use thr CLI version in terminal. As for restoring your profiles & msges you have always been able to export your database so to restore it on any device you can just import the sqlite database. However you have to set a password for the database you can't just import without knowing it's password.
I don't know the technicals around the protection on the db but it's probably listed in the docs somewhere on the github.