Not 100% true according to the description on that page. It just hides the banner if possible but it will automatically accept some or even all cookies and tracking if it is required for the site to function. And their choice if they accept some or all depends on "whichever is easier to do".

And functionality of the website could be social media or video embedding which might be "required for the site to function" in the eyes of the extension maintainers. But which will send data to Facebook, Google, and the likes. That could be okay depending on what your stance but a good thing to be aware of.