Napkin Finance is AWESOME. It's such a good way to engage people (even people who have learned these topics before) and get them to thoughtfully consider fairly complex topics. I also really like the added engagement the video provides, and that it gave an opportunity for me to learn more in just as captivating a way as the napkins.
One thought - have you incorporated any way for users to submit feedback directly on individual napkins? If it can be easy for users (ie short, work seamlessly, contribute to their positive experience), a survey at the end of the digital form of the napkins could be a powerful way to see which ones are working the best, and how to potentially tweak ones that people may struggle with more. Thoughts?