That was my concern too. So ssh is used for the initial handshake? BFHD. A lot of the interesting stuff happens afterward. The "how it works" page explicitly says this:

> ET does not implement any of the SSH protocol

That implies they rolled their own wire protocol. Maybe they did a good job (like mosh appears to have done). More likely not. I'd be OK using this on an internal network or over a VPN, but relying on it alone for security would be premature.