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

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 :)