I've been using it for comms with some friends and family when we're out of conventional network range. It works great, the pairing process is a bit of a barrier for securitu-muggles, but it works perfectly.
My only annoyance is that I can't run the mailbox program on a regular Linux/docker server.
AFAIK it's only available as an android application. But I haven't looked into compiling it locally or anything. It might he possible.