Honestly they should make it where if only one device can carry the chat database, then a desktop or server should be the primary device and then a phone or other devices can link to it. Their current solution of linking a mobile to a desktop doesn't really work (at least on iOS) because mobile devices have issues running background processes. I've never tried Session, and I don't know many people who use SimpleX. I do like SimpleX's idea of no accounts though (Session has accounts).