Ive just realised that the official one doesnt have the fallbacks that socket.io has. i.e. socket.io will work with IE8&9 (i.e. work with people stuck with XP) via its flash socket fallback.
Also, I cant get the oficial web socket plugin to work with socket.io running on node.js. I can write a js page which works with it, but cant get C2 to work with it. It never connects, no errors, nothing gets sent or received.