So is Fly good for small sites or is it good for huge sites? What's a big customer? For small sites my idea of a multi-region deployment is a single-region deployment that works in multiple regions thanks to the magic of the Internet.

I see this which mostly seems to be content sites. https://www.wappalyzer.com/technologies/paas/fly-io/ Same on the first forum result: https://community.fly.io/t/customer-success-stories/4882