This does a great job of breaking down different sorts of adversaries, including conventional NPCs as well as hazards, obstacles, countdowns, and so on. It also offers advice on how to put zones to good use. It's presented clearly and usefully.
Obviously, the focus is on adversaries, but I also use it for building allied or neutral NPCs -- adversaries of the PCs' adversaries.
You can get the basic mechanics and discussions from the excellent fate-srd site for free. What does the book add? Examples and artwork. The material you can find at fate-srd is only about 30% of what the book contains. The other 70% consists of 10 "spreads" (scenarios) that offer worked examples in the form of settings in ten different genres.
The spreads are clearly presented and each one hangs together nicely. The mix of genres is good. Even if you don't anticipate running one genre or another, you could still pick ideas out of the example spreads. You could probably reskin any of them for your setting of choice.
Each spread gives you about 8 pages of a scenario with some backstory. It presents a series of adversaries, using the toolkit's mechanisms, and discusses how they relate to each other and to the world. It tells you how you might incorporate the PCs into the scenario. Each spread has notes on how to use it for anything from a one-shot adventure to an on-going campaign. The spreads also offer notes on reskinning. There are no maps.
The artwork is good, but if the only added benefit to buying the book was the art, I'd pass. Seeing a drawing of Captain Pulaski, for example, gives me a visual, but I can get just as much out of the book without it. For me, the value of the book is seeing the adversary toolkit applied in practice in the form of ten adventure settings. (And you're helping to support the work by paying a few bucks.)
The book is all Fate Core. I run Fate Accelerated, but there's still value here. Much of the material is usable for FAE as it is. Where the toolkit discusses the Fate Core skills a Threat might have, for example, you can adapt that advice for constructing the character's high concept or other aspects. If you use one of the example scenarios, you'll need to convert the characters from Core to Accelerated. The Fate Accelerated/Core Conversion Guide can prove helpful there.
[5 of 5 Stars!]