I have all three of her books, including this one. They all include solid science and lots of helpful explanations. She starts with the basics and takes you through fairly advanced soapmaking techniques, including the properties of fatty acids, how to formulate a good recipe, how to choose additives for your intended purposes, etc. Another bonus is that once you have purchased the book, you have access to additional student materials and recipes that are behind the paywall on her website.
Although you could dig up most (not all) of the information for free scattered around the Internet, I like having a consolidated source of information that I could print out for reference as needed. I also found the author to be extremely responsive to questions through her Facebook group and the private email address she provides for that purpose.
In my opinion, these books are worth the asking price. You can also watch for coupons on her Facebook group - she usually offers 10% off around the holidays. You can try FACEBOOK10 and see if that promotion s still open.