In general, it is difficult to write and photograph yoga in order for it to be an instructive material. The nature of yoga is movement, and a lot is learned through one's own experimentation and from others.
The Power of Ashtanga Yoga is thorough. The book is broken into two sections: theory and practice. Even if you have other books which describe and show poses, the theory section is worthwhile.
Kino goes into detail about the importance aspects of the practice, interspersing small facts about her own experiences. You get about 50 pages of theory. She has many recommendations and suggestions for practitioners. She details the yogic philosophy in an easy manner without getting too complicated.
I can't really say that this is an introductory book to yoga. That is not to say that ashtanga isn't for beginners, but it would be beneficial to go to a class or at least watch a video of ashtanga and then go through the book. However, I think this is more a limitation of a printed book as a medium for yoga instruction.
One helpful appendix is the sanskrit vinyasa count of all the poses, which lists inhalation and exhalation along with the count.
I think her descriptions of the poses are done well. She really goes into a lot of detail and while reading, everything made sense to me. I didn't find any portions where it seemed to skip a step.
There are modifications for beginners and advanced practictioners.
Kino has a really positive attitude, which comes through in this book. I have put this next to my yoga mat and have been referencing it every day since I have received it. Because it's a larger book, the book and the pages stay open by themselves - quite handy while practicing.