For just $4 more one gets the Ebook. Buy both and it’s like getting a $6 discount. You could also look at it as Buy the Ebook and for just $10 more getting a physical copy of the book. Shipping is $5. Special Priority shipping is $10.
$6 discount / $25 discounted cost = a savings of 24% for buying both.
For $25 I ordered both the book and Ebook. It is unclear how one gets the Ebook. There was no download included at checkout. That part of the story is to be continued.