Not customizable at all, has a few options and anything over 5x or below 0.25x will work badly. 16x has no audio and 0.1x doesn't play at all. The UI also doesn't feel comfortable and you need to be clicking on it instead of hovering to change, but if you hover, it will pop up.

Great design and UI.
However, I'm not sure why, but the extension simply stops working from time to time.
Sometimes it works no problem for a few days.
Sometimes I open a new video and the extension is gone, so I have to deactivate and activate it again... but it's gone by the next video.
Also, deactivating and activating it causes the UI to appear multiple times on videos where the extension was still active (only one works)