As the words "Royal Path" in the title suggest, this book and the system presented in it are not for everyone. It is not the place to look for information on (Neo-)Tantra. The system presented is neither entirely original to the authors nor entirely original Tantric practice and belief.
Certainly, much of this information can be found elsewhere. It recieves 3 stars, however, as it is a good collection of information and techniques, and I found their discussion of various beliefs both refreshing and thought-provoking.
Two people who purport to be teachers of Wicca (decidedly grumpy, arrogant ones at that, judging from their writing style) have slapped the "Tantric Yoga" title on some rather jumbled fundamentalist-feeling Wiccan teachings, presumably for marketing reasons. Shame on them, and shame on Weiser Books, a usually reliable imprint, for letting them get away with it. Check out books by John Selby, Karla McLaren, and Jonn Mumford for a real introduction to Tantra and Kundalini.