Bought the book. Read the whole thing. Here's my thoughts.
1) Not a book about IF. More about his personal journey and the realization that freedom (aka, flexible dieting) is the key to adherence. IF just helps some people with adherence. I really enjoyed this part of the book. He's a good writer.
2) The diet is really just The Rapid Fat Loss Handbook 2.0.
So he comes to the conclusion that we need way more protein than previously thought because [reasons]. End result is typical "calculate your calories, subtract 500/day." But then, get 50-60% of those calories from protein.
When I run those numbers, it puts me exactly in the 1.5-2.0 g/lb LBM range that RFL recommends for weight training.
Eat lots of fibrous greens (like 1kg broccoli/day), some fruit before/after training. Be flexible with the rest of your diet (within reason).
So really, its just taking RFL and adding in enough "other stuff" until it becomes a sustainable long-term fat loss program.