when this goes public the creators are more then welcome to shoot me a message on GitHub and I’d happily remove it.

The only real load cost is on their CDN server which is probably designed for high traffic environments.

I can also modify the user agent of the HTTP requests so they could filter them based specifically on this application if that’s an approach they’d be okay with.

Why not just message them at their contact email address and ask in advance if your assumption about their CDN server is true, you should set a specific user agent etc.? Then they wouldn't have to potentially waste time on figuring out what's happening, writing and deploying filtering/rate limiting logic or finding the repository and contacting you on GitHub.

Have you asked the operator of those sites if they are fine with this?

It would be a shame if they were to be taken down because of people scraping the site causing too much traffic costs or something.