Used to be good in the past. Now not so much. While there are a lot of great options i consider a must have, sadly it makes youtube tabs extremely heavy and also near unusable. The YT interface becomes laggy and tabs freeze constantly.
Worse is that it happens on both Chrome and Firefox on two different PC's. (even worse is that performance issues have been present for a long time now, they just got worse and worse over time with each update)

Since the last update, i can't even open the settings anymore, it just says "asking your browser what settings you made here before" (on the FF PC) so i can't even export my settings (or more importantly, the watched list) anymore.

Sadly all of that means that the addon is unusable and simply does not work as intended anymore.
I hope it will improve at some point, but for now i can do nothing but to remove the addon for good, from all my devices.