Aye. I finished his novel in a single day. Couple of thoughts. Dude is real religious, apparently thinks everyone else is either real religious (or working at being real religious) or else they are a very bad/dangerous person.
His thinking is not very flexible. He has his way, and that are not flexible. Boris phrased it quite well. If you are not prepared to follow his type of thinking, you may find the book somewhat but not extremely useful. I am not saying it's worthless. I'm just saying it has limited amounts of use.
If you read the novel, be prepared for every stereotypical right wing fantasy. From the only liberals being communist cannibals to the UN invading/occupying the US to "Wolverines" overthrowing federal government slash UN globalist slash Jewish banking conspiracy. I noted the half hearted attempt at tokenism. Those parts made me physically cringe. Because a) it's such a simplistic view of the world that the stupidity is actually painful and b) it shows the very sharp limits of the guy's knowledge. If the above sounds awesome, it's not written as well as you think. The characters can and are often flat/hollow. The action scenes start getting written better towards the tail end, but the ending is badly written and abbreviated. "And then we wins!!! And everyone accepts religion, and we's haves gold standard, ands the economy magically fixes itself, and the wimmin know their place, ands the evil Europeans pay us to allow them to leave, and we add fifty billion Constitutional amendments" Etc, etc.
The guy may or may not be very knowledgeable about survivalism techniques and equipment. But he bases his entire life around theology, more so than anything truly objective. Yes, yes, he no doubt studies all kinds of niche "survival" skills. But at the expense of generalist knowledge of banking, commerce, economics, politics, and foreign culture. Among several dozen other fairly major spheres of knowledge. It is very apparent that the guy has significant deficiencies in his scope of knowledge. But in fairness, the areas he has applied himself to, he is quite knowledgeable.