Badly implemented and relies on it's own lyrics database powered by fandom and under some weird UUID based on track id's rather than a search for terms.

Terrible sadly, avoid this one.

While the idea could be good, it would require a lot of users to actually fill the wiki with (correct) content, but at the same time this would also bring a lot of trolls, ruining it.
I think added lyrics like this should just be done through YouTube captions instead, which kinda does the same thing already, but natively within YouTube. It just is not really used for song lyrics so far.

Edit: Alright. I want to update and rise my review / rating slightly, just because I at least gave this a proper try myself. This is more or less the only YT lyrics addon that at least works, assuming there is a decent entry of the song you want to listen to. So I quickly made one for myself and the result is pretty decent. Feel free to check this song out if you want a demo:
https://www.youtube.com/watch?v=U6rv5qi8-8s

Something the screenshots did not show: Just add a timestamp with no text to remove the previous text, if you happen to get a quiet spot within the songs.

Small edit: Less-than signs seem to break it a little, at least for the line it is used in. So no text hearts unfortunately.

I didn't get it to work.

Update: I disabled annotations, and that is required for this extension to work apparently. I enabled them and now it works. It's a nice integration idea, but it should have been mentioned that annotations are required for the extension to work.