I'm using this Addon for years now and it has always worked perfectly until very recently because since about a week ago, because I'm getting Ads at the start of every 2nd or 3d video. Reloading the tab does usually help to make the ad go away, sometimes I have to reload twice.

(BTW, I'm also using the "Improve YouTube! (Open-Source for YouTube)"-addon from code-for-charity which - among other things - should block ads as well, and that doesn't work either at the moment.)

So I'm just rating this add-on with four stars - for now.
But as soon as it does work as good again as it did, I'll upgrade to a full fiver again. :-)