I'm not one to write reviews often but I feel the need to for this add-on. Firstly, my biggest gripe recently is YouTube's UI "improvements".
This add-on lets me clean up the home page's sidebar to get You(history, playlists, etc) back where it used to be. I then switched Subscriptions to be on a link below the Home link, easing that burden so I'm not hitting a subscription instead of history like I have been lately. Also was able to make the videos and thumbnails squares again, which I love.
I just started playing with the add-on, so I might not have seen it or it might not be possible to do, but the only thing I wish this included so far is to remove the drop-down menu next to watched videos in History and bring back the X that was next to them for the longest time.
Aside from that little thing, I absolutely love this add-on, and the developer genuinely has my highest respect for this. So thank you!