I’m on my third book from Modern Serial. (Disclosure: I know @andrewedstrom). It works great for me, and getting the segments via email ensures I don’t forget to read. Andrew has also been super-responsive to feedback and feature requests.
Are you aware of <a href="https://www.serialreader.org/" rel="nofollow noreferrer">https://www.serialreader.org/</a>? How would you differentiate yourself (besides email VS app)?
Interesting! Clean UI, good execution. Am I correct in thinking that these are all copyright-free books? Also, which vendor do you use to send emails and how many customers do you have so far?