I just installed this on my Chromebook with Ubuntu, and on my EC2 instance. I've been very frustrated with the lag I was experiencing while typing in the shell, due to high/variable latency. In my very preliminary testing over the last hour, this has solved my problems almost completely.
Security is less of a concern because I'm running OpenVPN to my instances, so the UDP traffic mosh uses is encrypted anyway, and not open to the public.
One issue I did notice is that irssi isn't refreshing quite as quickly. Seems to lag behind the conversation a bit. I'll have to troubleshoot. I wonder if running byobu/screen is part of the problem.