in this book, chogyal namkhai norbu presents a detailed explanation of a medieval yoga text, as informed by his receipt of oral transmission. he makes no mention of whether in doing so he violates tradition, or whether an initiation is considered necessary to practice the exercises.
in general, tibetan buddhists are required to complete a series of purification exercises that last about two years before undertaking the higher levels of tantric instruction. one can only assume the practices in this book are an exception, because norbu does not discuss that point. there's a brief, obligatory statement at the introduction of the text stating that one should seek instruction from a qualified practitioner, but aside from that the reader is not discouraged from giving the material a go.
the text itself is basically a manual, presenting the exercises verbatim without frills or discussion. one might infer that the text was intended for an academic audience if it weren't for the fact that the instructions are so clear and specific. perhaps it was intended as a reference for the author's students, but if so that statement is not made anywhere.
if you are like me and are fascinated by the various schools of yoga and their practices, you will find in this book a real treat. it presents a highly esoteric system that is very different from typical studio yoga. the exercises themselves, however, are quite complicated, and it is probably unrealistic to think you can learn to perform them correctly from this book. you should probably check out the videos available freely online by norbu's students and others, under the titles "yantra yoga" and "trul khor." there is a very specific rhythm and form to the exercises that cannot be gleaned from the text itself. if the author's assumptions are correct and these exercises act to free blocked energies in the subtle body, performing them incorrectly could conceivably lead to temporary psychosis or other problems.