Neat and fun PR stunt. Tech needs more of these!
SGI did this almost three decades ago:
https://web.archive.org/web/19971210213248/http://lavarand.s...
...harnessing the power of Lava Lite® lamps to generate truly random numbers since 1996.
According to https://www.lavarand.org/news/lavadiff.html:
Seed production rate was about 8000 bits of seed per second on a 200 MHz SGI O2 under IRIX 6.5.
The patent has since expired: https://patents.google.com/patent/US5732138A
(And Cloudflare re-implemented it, seemingly starting just after the patent expired in 2016.)