It does seem to be the most commonly used WebSocket polyfill around. We also use web-socket-js [1] for fallback. But Version 3.0 of pusher-js [2] will remove that.

One negative with SockJS has been the complexity of the fallback approach on the client (the browser). Especially when it's only for 8% of connections. A single simple cross-browser HTTP-based transport would remove the code complexity and reduce the file size.

[1] https://github.com/gimite/web-socket-js [2] https://github.com/pusher/pusher-js/tree/r3.0.0