I play D&D 5e instead of Pathfinder (though I am very interested in trying out Pathfinder 2e once it releases), but I got a PDF copy of this thanks to a Humble Bundle sale. Obviously, this book will be immeasurably useful to Pathfinder 1e GMs, but there's enough crossover between the two systems that much of the stuff in here can be retooled for D&D, and a lot of it is generic advice on how to run the game and brainstorm aspects of a homebrew world, which is always appreciated. I especially liked the straightforward advice at the beginning of the book on how to handle the social aspect of GMing - AKA scheduling your players, dealing with conflicts at the table, interacting with the various types of personas (Rules Lawyers, Flakes, Divas) that come up in RPGs, etc. This is the sort of thing that I think a lot of Game Master guides skimp on in favor of heavy world-building chapters, but the truth of the matter is that most GMs are going to want advice on handling problem players before they want advice on how to construct an intricate cosmology. The D&D 5e Dungeon Master's Guide could definitely use this kind of thing, and I imagine if it had it, we'd see a few less "HOW DO I HANDLE THIS RULES LAWYER DOUCHEBAG" threads on Reddit. Last but not least, the more advanced rule sets in here for handling stuff like drugs, in-game natural disasters and especially CHASES are great stuff. Worth at least a skim-through for all GMs!