I'm a longtime customer of Gary's books, in both electronic and print forms. They aren't perfect, but they have been very useful to me and well worth the price -- especially the e-book versions.
Most recently, to prepare for a couple of complicated live-event shoots that included several different successive scenarios (indoor, outdoor, posed, candid, on- and off-camera flash, light, dark, etc. all in a rush), I loaded up the book PDF (along with Sony's official electronic manual for the camera) into AI. Through multiple successive queries and conversations, I was able to produce clear, step-by-step instructions on 1) what settings, lenses, and accessories to use for each scenario, and 2) how to set up my camera (1-2-3 on the dial, custom buttons, flash timings, etc.) in advance for the easiest and quickest workflow in this specific sequence of situations. (This may be old hat for many of you, but throw in a global shutter and multiple speedlights and it can get complicated very quickly.) I also had it create a phone-screen-size "cheat sheet" for what to do at each location switch. Needless to say, prepping with Gary's book as a source was enormously helpful.
I used a Google Gemini Gem to set this up, but you could use NotebookLM (recently renamed to Gemini Notebook) or any other AI setup that allows you to load up sources and restrict the answers to those contained within or deduced from them. (When you get into the nitty-gritty of a camera's capabilities and quirks, there aren't many reliable sources that stick to your model specifically.) On a few occasions when the suggestions seemed unintuitive, I responded by asking if Gary Friedman would really do this sort of thing. The responses quoted directly from his manuals -- and helped me solve the problems.
Hope this is helpful to somebody wondering if or why they might want an enormous book like this.