http://andymartha.com/book is my first e-book, built on my modules for Drupal.

Originally, this book was on Google Play and Amazon, but, because technology moves fast, the fixed epub version information went out of date quickly. Because Drupal is easy to update nodes, I can still publish this for sale and update it whenever I need to. Plus, users can buy only what educational content they need for the moment.

I did everything myself: theming, module writing, book-writing, site building. What should I improve upon?
The background is a picture I took in Chicago. The book is about how to build an app using city (of Chicago as example) data for general population benefit.
My goals were text-readability, mobile friendliness, and done in a weekend or so (site-building, not book writing).

This website was made with the same modules/base as http://dev-biolithic.gotpantheon.com . (I just themed both differently). That site is the demo/homepage for these.
There are two modules shown there.
1) pay-per-chapter type, in which the writer writes a teaser and full body of a chapter, and users can buy that chapter to view
2) pay-per-membership type, in which the writer writes a teaser and full body of a content type, and users buy a membership to view that content type

It will be:
1) a distribution (custom theme + all the modules pre-installed) for you to download.
2) each module for download separately on drupal.org (you can see them on my profile https://drupal.org/user/1204604 ).

Would you use something like this A) "out of the box", or B) as a module on your site?
Is it easy to use?

You can watch a video of the functionality if you so desire.
http://www.youtube.com/watch?v=QGwMRRxZMRA
Thanks for reading, post your thoughts!
Andy