At the same time I agree with his idea that a knowledge base + spaced repetition is a good combination, however outputting spaced repetition into a 3rd party app is not a good idea.
I see that burtonator is trying to push this product here every time a relevant discussion pops up, I don't have an issue with that. But I do think that this product is a long way from being useful for me in a daily setting. Right now it's nothing more than an electron wrapper around pdf.js and knowing how far I read a pdf.