That won't really work for the scenario they try to "protect" against.

When you copy some js files that include their license checking code to your server and them serve it to your clients, your clients need to block qeys.io, not you.

You can instruct clients to do that of course, but it's rather easy for one of them to forget and the copyright holder is noticed.

Still, blocking qeys.io by default on your system sounds like a good idea :)

You will still get caught because google will crawl your site which in turn will make a request to qeys.io and then I will get a notification with something along the lines of "Customer jlebrech is using an unlicensed version of your software on unlicensed-domain.com". The purpose of this software is to report the copyright infringement of the host, not the user.

Or a CSP header server side. But still something the average client will miss, at least at first, and trip the alert.

Exactly my thoughts.