It does look like you have to download a 10Mb js file, but once that is downloaded and cached, it uses a websocket to communicate with the server on the backend

It does look like you have to download a 10Mb js file, but once that is downloaded and cached, it uses a websocket to communicate with the server on the backend and only necessary text will be sent to the browser. I don't think the bandwidth requirements should be too much more than a terminal editor over ssh.