Concerning getpolarized.io: I just watched the first video on the front page, and at 50% I was like, okay 'reading-progress tracker' I don't need that and was about to close it, but instead, I skipped through to the end, and then I heard 'Anki'.

Boom, spot on. Being able to create Anki flashcards while you are reading new content is pretty cool, and much more useful than the whole 'non-linear reading progress' (most documents are meant to be read linearly, and my PDF reader opens a file at the position I closed it).

Now I will check it out ;-)