Eddie Bravo's success, to me, closely parallels that of Royce Gracie in UFC, in that they were both successful in finding a powerful niche. Royce was able to exploit an area largely neglected by other disciplines--ground submission grappling--and beat bigger and more atheletic opponents. Eddie, likewise, was able to find his niche in a position--half-guard--that other BJJ practitioners avoided or did not focus on. Having watched his celebrated match with Royler a few times, it is my opinion his victory actually is more attributable to his half-guard skills, which frustrated Royler into being careless, than his rubber guard. Certainly, without his half guard, Eddie would have been mounted within a minute into the match.
The half guard portion of this book is truly remarkable. The moves not only work, but have already become classics. Even if you have no interest in becoming a half-guard expert like Eddie, you should become familiar with those moves because you will be defending against them sometime in your grappling career. The fact that Eddie was able to hold off someone like Royler in his half guard for five minutes should tell you how effective the moves can be if you are unfamiliar with them. My recommendation is this book is a definite buy just for the half-guard materials alone.
I am less enthused about his rubber guard. The rubber guard is a decent way to hold off an opponent and create some breathing room but I don't think it is revolutionary. Eddie has made conflicting statements on the issue, on one hand advertising the guard as being revolutionary but on the other hand admitting that rubber guard, like all guards, is inherently risky and ineffective. It seems somewhat more effective in no-gi, but that is not surpring because it was designed for no-gi. Regardless, I think it definitely belongs in the "good to know" category, so you can defend against it, even if you are not interested in using it. If you are interested in learning about the rubber guard, then certainly I can think of no better authority than its creator.
The book as a whole is easy to read, with color photographs that makes it easy to distinguish the limbs of the practitioners. It even has a flow chart. Overall, one of the best executed martial arts books I came across.
As an aside, I am a bit astounded by other reviewers' focus on the book's preface. Certainly, Eddie advocates the use of marijuana but I am not sure why this seems to offend many. He sincerely and strongly believes that marijuana improves his BJJ game. Then it would seem only natural that he would recommend its use. It's his book and he can say whatever he wants to, just as a reader is free to disregard or rip out those sections. I certainly do not think his belief on the issue affects the content of the book in any negative way (except for the funky names). I think the issue should not be given much thought.