I don't believe it's identical at all. Eternal terminal is a TCP-like abstraction that adds another layer of tracking and acknowledgement so that the reliable ordered byte stream can be reconnected and resumed. Mosh is more like a video codec mixed with a terminal that knows how to do limited, speculative local echo that gets subsequently corrected once the display round trip is complete. They're fairly different in approaches.

For example eternal terminal has to send all of the bytes in order, so more output requires more bandwidth. Mosh only has to redraw bits of the frame that have changed, at a presumably adaptive rate -- you could scroll a hundred megabytes of text by really quickly, but only need to send a few screen-fulls of updates, which is of course why it doesn't allow for regular terminal scrollback.

> It works in identical fashion to mosh.

No, it doesn’t. The best way I understand it is that mosh syncs a “view” of your current session, whereas et just sends everything. In practice, what this means is if I accidentally cat a 5GB file, mosh zips past as if I were working locally (and ^C works!) whereas et completely locks up until the file reaches its end. That said I still prefer and use et daily due to the scrollback and tmux -CC support.