Hang on: The Tee Spring code checks if GA is there and works without it, the website breaks because Ad block replaces GA with a fake object that doesn't have the same API. Perhaps some companies have the resources to check if their websites run with different ad blockers, but expecting websites to work when plugins are replacing and breaking running code is a big ask.
Ignore it at your peril. If you want to make sales, you need to test the ways your prospective customers want to buy.