To me this seems like Mosh, but worse. I think that each project's approach has different strengths. For me, the best part of Mosh is the intelligent, asynchronous handling of type-ahead. Mosh feels really snappy, even over poor connections. I'm not bothered by needing to run Tmux on the remote for scrollback; I do that anyways, and I have no need for this fancy "control center" mode.
My big frustration with both Mosh and ET is that neither expose a data communication channel along side the PTY. I use SSH for port forwarding, Tmux paste buffer sync, file transfer, and SSH agent forwarding. Without those features, I'll always need to use SSH/Autossh along side these tools for my other SSH use cases.
It gives you native scrolling / tabs in iTerm2 which for me was a huge plus. I hated using the keyboard for copy and paste in TMux. That's just a personal preference though.
It is not clear from the error that you were missing libsodium. I don't remember what was my error anyway, I'll try again later. But I can't even find libsodium on my apt.
You may be running a distro that doesn't have libsodium (such as ubuntu 14). In this case you have to grab libsodium manually and build et from source.
