Hmm... The examples are running on the free tier of Cloudflare Pages Functions. I should be dramatically under any CPU/networking/transfer limits. And it should scale up as needed.
I just tried all of them now, and they did load. What is the exact error you are seeing? Just a blank page or ???
If you mean that the input box for "copy to clipboard" is empty, that's because the feed doesn't have a "self" link, which the stylesheet needs.