Very slow (even by youtube standards), whatever what the dev will say: sometimes takes almost a minute to load a youtube video, and often will fail to load the full page, with the comments.

Very buggy: again, often failing to load a page fully, the mini-player suddenly not appearing anymore when scrolling down, or among many others, the limiting to H.264 not working reliably (to be fair, it only reliably works with enhanced-h264ify, whichever main youtube extension I use). Even the menu is buggy: the search bar will always cover the link to go back in the menu (so one has to close that search bar again and again), and if used in the extension panel (as opposed to using it pinned), it won't even fit the window properly, lol!

Fortunately, I discovered a little used extension (Tweaks for youtube: only about 3k users, which is baffling), that is great where Improve youtube isn't at all. I tested them all, and that's the only one I'll keep.