The original from SGI back in the mid 90's, before CPUs had RDRAND instructions etc... was a an actually practical solution.

At the time I was at the Internet company that originally got online-gaming banned in the US, we were looking at CCDs and Cesium emitters that required a license etc...

While I am not sure, it seems cloudflare basically implemented one after SGI's[0] patent expired.

The patent and the licensing cost and adding SGI was a major blocker for us doing it, the startup closed before we found a real solution. But the best PRNGs like Blum Blum Shub were way too slow at the time. But things did improve quickly at that time.

[0] https://patents.google.com/patent/US5732138A/en