The book explains the Master/Slave dynamic well.
Unfortunately, the author gets tangled in his own ego.
He apparently thinks that BDSM relationships are above "vanilla" relationships, and writes they are special, a calling, have more meaning and a better structure than non-BDSM relationships.
At the same time he explains a lot of things an ordinary couple therapist would advise (open communication, empathy, self-reflection, etc.).
It boils down to a "I'm a special snowflake because I don't get therapy for my control issues and instead incorporate it into my daily life with willing, equally-misguided people" handbook.
He's also gendering a lot, considering women the standard submissives and even recommends the book "Men are from Mars, Women are from Venus" (for better understanding each other!), which enforces harmful gender stereotypes and is incredibly sexist.
The author mentions a couple of times he's 70, so it's pretty clear due to his generation, and their limits in gender politics, he has a very narrow view about the different roles (and equality) in a relatonship.
This book is the result of an old man writing about his comfort zone.