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That looks like a very high quality shim, so that is good.

However, why would I want to use a shim over websockets?

I'm not sure how much of this still holds true, but here's a few reasons you might want to stick to HTTP: https://speakerdeck.com/3rdeden/websuckets

tl;dr websockets can fail in strange ways on mobile and when passed through proxies and corporate firewalls