Disclaimer: I received a free copy of this product for the purpose of writing this review.
Also, I love me some creepy books. Seriously - I've got a huge soft spot for anything even vaguely Lovecraftian, and I've even thrown the occasional grimoire into my campaigns somewhere. This is an 8-page product, with six pages of content, a cover, and as always, the OGL. Inside are ten spellbooks (most useful for prepared arcane casters, obviously), each with a different selection of spells. They range from the cheap and simple (The Baseborn Baron) to the genuinely powerful (The Hypostatical Golden Fragments), and most of the books in question have preparation rituals that give some interesting bonuses. They also have physical descriptions for flavor, as well as brief histories that can be used to properly integrate them into the setting.
Note that most of the books are dangerous, and can cause sanity loss among characters - they're best used with those mechanics in play, and their examination periods mean characters will need to spend time studying their blasphemous contents in order to make use of them. All in all, I like it - these are easy enough to drop into any campaign setting, and they're just creepy enough to serve as plot hooks for your next adventure. I saw no meaningful errors and everything looks to be in order, so full marks overall.