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?
I use Sendgrid to send emails, which has worked great so far although it took a while to get my account fully set up.
Re: customers, so far I've had more than 10 and less than 1000. One encouraging sign is that many people are coming back after finishing their first book and buying another.