A fantastic app. It saves your preferences across all embedded video formats too (bar a very select few - looking at you Crunchy Roll) which means which means you don't need to reset your speed to 2x every time you delete your cookies/cache, or visit a new website!
I watch all my videos at 2x speed now and I was shocked how much time I saved. It no longer takes me most of the night to work through my YouTube notifications, and has left me so much more time for project work during the week.