I take a somewhat dubious view of people who sign themselves off as Grandmaster of a tradition. It implies that they are the top of an organisation which is worthy of the Knights Templar and this book will probably be more about them and their beliefs than their subject matter.
Sadly that is mostly what this book is about. You learn a bit too much about the author and his experiences and little about the club itself. If you are hoping for an understanding of the mysterious Hellfire club founded by Francis Dashwood you are going to be disappointed. Indeed much of the information on the buildings can be found in pamphlets and that which is not, is pretty much a flight of fancy. For example he notes correctly that the font in West Wycombe church has a serpent rising up its stem to attack a dove. He connects this to a letter in which members of the Hell Fire club were expected to go to the church and implies the font was part of the ritual. Yet the serpent of Satan rising up to attack the dove of the holy spirit is fairly bog standard Christian imagery which you would expect to find in a church font. The dove is not, as the author suggests an image of goddess Venus, who was an important part of the Hellfire ritual.
The author himself admits that we know nothing about the rituals of the Hellfire club and anything he can come up with is just a guess. Unfortunately his guess is a mish-mash of new age thought, and half thought out occult and masonic ideas. If you are going to base an esoteric system on the Hellfire Club you should at least attempt to use the systems which were available at the time. You would not see Francis Dashwood talking about Chakras or karma. These ideas did not really enter British esoteric thought until much later in history.
Writing wise the book is all over the place. The author claims that this is because he is taking a mystical approach to his writing. In fact it is just bad and unfocused. An editor would have knocked some sense into this, but I am not sure if it would have saved it.
Sadly there is nothing to suggest that the Hellfire Club was anything other than a fairly standard drinking club from that historical period. Its rituals were probably similar to those of the fraternities still seen in US universities such as the Skull and Bones, and little to do with anything occult. If it did have anything to do with the occult, then it would have been closer to Francis Barrett's the Magus, rather than this vision, which is more Helen Schucman.
I would think that anyone interested in the Hellfire Club, who knows a little about occultism could use studies such as this one The Hellfire Clubs Satanism Societies
and come up with something a little better. Sadly this book is one for avoiding.