Martial arts are filled with ego. I talk to people from various martial arts on a weekly basis and what most of them have in common is they think their particular style is the best. Really it's a load of old bunk. I imagine the high rating for this book comes largely from people who train in Bujinka...
This book is interesting and there is some good information in it but it's not for a wide audience. The images in this book are disappointing.