The add-on ignores the http-equiv="Onion-Location" meta tag in the HTML head and uses a static collection of manually collected onion addresses instead. So, you're only notified of very few websites' onion services.

Moreover, the few notifications that you receive are unhelpful because they suggest you v2 onion domains which were deprecated years ago and don't work anymore (which the add-on doesn't know).

That means, the add-on is completely useless currently.