Have it installed for a few weeks now, it fails for many domains. If you click a link from example.com to example.org, it will already mark example.org as 'potentially tracking you on example.com' (because it sent the referer of example.com to example.org
once).
Also it reports nearly every domain I visited in the past weeks to be tracked by lesswrong.com, which is rather impossible.
Lastly, it gets cluttered very fast. Not within 5 minutes, but a day later no user could make sense of it anymore. There should also be a clear overview with things like top domains (which would be Facebook for their Like button, Google ads and analytics, and probably more).