This and every item like it I've gotten from this genius of a man is worth the tiny bit of invested time to read, and more money than is asked. I got all the "pay what you want" ones for free to try them out, as I'm low on funds right now, but I intend to go back and buy them proper when I have some bills paid off. If I had to value this and his similar books, I'd say $4-5 easy.
Not only is the content solid and extremely useful for any roleplaying system, but the way it's presented is cleverly minimalistic and very easy to reference. I absolutely hate reading, but these PDFs are a pleasure to read. Excellent publisher, this good fellow.