Personally, I'd rate this book around a 3 or 3.5 just because I've been doing my own research on persuasion for a year or so now. I've read a lot of books on techniques and little things that persuade people to take certain actions. This book is basically a summary on all these different kinds of techniques.
A lot of the things I already knew or had learned in another book, but it was nice to have the author pertain it to web design and design principles. For someone who is just a designer or web focused copy writer looking to dig into this persuasion world, this is a nice place to start. It gives a good overview of all the different aspects of persuasion design, like getting people to click a certain button or feel a certain way when designing a web page.
Some of these things designers may know instintivly, but it's good to have those instincts re-inforced by someone else. At only 16 bucks I would recommend a purchase unless you're really already deep into neuro-design or persuasion techniques.
If you're sort of new to the field like me, you'll enjoy the insight the author gives, though it is a quick read. I think there are only around 200 pages total, if that. She doesn't delve too deep into the topics either. I would have liked to have seen some more case studies perhaps and more detail on some of her research. Possible for a second book she could go more in depth, as it is now it's a great read, albeit a little short.