This book must be taken in the spirit it is written, which is to expand upon Reiki's path into the west. There are arguments around the rewriting of the history of Reiki to include aspects thought not to have been originally taught by Mikao Usui, such as the kotodama, variations on transmitting attunements, and the insight into Usui's experience that led to the formalization of Reiki as a system. I completely respect those arguments and feel a sense of protection for the traditional study and the culture that created it. With that in mind, understand that this book challenges facets of that tradition. If you are not comfortable with that, this book is not for you.
That said, I find it engaging and well-written. I cannot speak to the validity of Reiki's history; therefore, I cannot judge the accuracy of this work. It is compelling and carries with it a sense of honor and respect for the Usui tradition, despite its deviations. This book could appeal to someone beginning Reiki, but it is more likely to address questions and curiosities of a seasoned practitioner, as well as pique established methodologies.