I dig the demo app, seems like a great marketing tactic for the book.
I personally won't buy the book, not because of you or the quality but this tech doesn't pique my interests.
I think you need free content that eventually leads back to the book. We don't know you or if the book will be worth the purchase. The blog posts also helps with SEO.
Another suggestion, add about the author on your landing page. Who are you and answer the question what qualifies you to teach us?
I couldn't find a price for the book, even if it isn't ready price will be a leading factor which sometimes maps to quality of the product.