A link to the book
You probably don't need to read past the headline, but, here are some specific thoughts (not really a review) in a very non-specific order:
1) Nowhere does the book claim to be for advanced or experienced runners--and indeed, it makes frequent reference to those whose goal is, say, a 30-hour 100--but I'd suggest it is better suited for that demographic. Not just because the training is intense--though it is--but because there isn't a ton of hand-holding. There aren't any plans. His argument is, he can't coach you without coaching you. And so, if you don't have a coach, you have to coach yourself. Newer runners may not have the experience needed to make smart, consistent decisions, however. And they certainly might not have the confidence to do so.
2) The book helpfully avoids outlandish claims, and guru-ism. Which is not to say it's precisely typical of ultra-training advice--it isn't--just that Koop cites the hell out of his claims. To put it too simply, he's very much an "exercise science" coach, not a "because this has always worked" coach. Again, that's a bit of a false dichotomy, but is nonetheless useful is describing his approach. If you're the sort who believes the way to train for ultras is to run as much as possible, because shit, it's a fucking long footrace, what else would you do?, you will probably be sick to death of the extensive physiological justifications for everything.
3) So, about that training. It is intense. In specific blocks, it even makes some of Daniels' more rep-intensive phases look decidedly moderate. (Though his workout as far more simple. You really can memorize everything you need to know about his workout structures in a few minutes, and indeed, it's all in one small table. This, to me, is a feature, not a bug.) Koop's contention is that, to force an adaptation--especially in an experienced athlete--you have to apply increasingly severe stress. One hill workout a month, performed at a mediocre effort, isn't going to provide significant stimulus. And that is, primarily, his concern: Build the biggest engine possible, then--and only then--get specific. Historically, one might call this base building, and put the focus on high-end aerobic running. Lydiard 101, basically. Koop is more like Canova, though, in flipping this prioritization scheme. Get fast, then work to extend that speed. Some will note--and have--that his blocks are unsustainable. He'd say that's the point, that if you always train similarly and cautiously, you won't get much better.
4) I'll give this a separate section, just for emphasis: As much as his focus on intensity might momentarily lead you to believe otherwise, his is not a low-volume approach. But the volume exists as support for and a result of the quality work, not as a goal in and of itself. He treats long runs--usually the keystone of ultra-plans--similarly: Useful, but not wisely pursued at the expense of quality. His argument here is essentially--and this is where I come back to this approach probably being best for someone who has been running for a while--that high mileage and long runs yield benefits over months and years, not weeks. If you've been running 50 miles a week for five years in a row, he would suggest you're unlikely to get significant physiological benefit from a plan that focuses on long runs (at the expense of other sessions). To him, long runs are for fueling and pace practice, and building confidence. These things are valuable, but inessential.
5) You'll probably disagree with some of his prescriptions, but he does justify them with lots of citations. For those who like a "why" with their "what", this will be appreciated. Being in this camp myself, I especially enjoyed his explanations of what each type of run he prescribes is supposed to do. It is, in my estimation, the best lay-person primer on endurance physiology out there. (Magness' The Science of Running is more extensive, but probably beyond what the average person wants to wade through. The formatting, editing, and writing also fall a bit short, comparatively.) Perhaps the best thing about this approach is that--although he hates this metaphor--he's teaching you to cook, not just handing you a cake. Whether you end up opposite every one of his conclusions, you'll probably learn quite a bit to apply to your own training.
6) Ultras are more than fitness, however, so there is extensive focus given to foot maintenance, how much to eat, etc. Being honest, I... skimmed these parts. They're useful, but less interesting reads (to me). Same goes for the several-page treatments given to some of America's most famous ultras. Were I going to run Leadville, I'd appreciate the course knowledge and tips. But I'm not going to, so.
7) This is a professionally published and co-written book. It's technically sound. In my first quick read-through, I noticed only one obvious typo. There is a slightly irritating tendency to reference a table that one has to turn a page to see--in academic publishing, we call this a facing pages violation--but that's never too obtrusive. There are little anecdotes by some of Koop's more noteworthy athletes--Dylan Bowman, Dakota Jones, Kaci Lickteig--inserted into the run of text. While this does break the flow of reading sometimes, I suppose many will find these sections interesting. Given Koop's stated disdain for n = 1 data, though, they do seem a little out of place.
8) Koop does dismiss rather casually of a lot of ancillary concerns. He doesn't have a stated opinion on shoes or diet (other than that LCHF is misguided, insofar as it compromises intensity), and believes cross training is almost always time that could be better spent running more (or recovering from harder running efforts). Personally, I think there's quite a bit of evidence that strength training supports endurance adaptations, and provides unique benefits that running more wouldn't cover. Others will swear that cycling saved their running, that optimizing fat burning--by eating a high percentage of it--is the key to endurance, etc. But I don't suppose we're ever going to have all the answers to these things. The book claims to provide Training Essentials, however, so perhaps Koop would argue these are fringe concerns in any case.
9) You should buy this if you're a training/exercise science geek, or an experienced ultrarunner, who thinks they've maximized adaptations from a traditional (mostly easy) volume-focused approach. In terms of marathon training books, it's probably most similar to the Hanson's approach--speed to strength to specificity--but with way more science words, and clearer periodization. I'd say Canova is perhaps even closer, but he hasn't written a book in English, so that's something of a guess. Still, the focus on quality and intensity over volume (once a runner has, to use a Canova term, built their house) seems similar to me. That is, it's nice to have a base. But you have to build up and out if you want to fit more shit in, eventually.
10) I don't know if this is the best plan, or set of principles, or whatever. I'm not a scientist or a coach or fast enough to have an official opinion on such things anyway. But it's a good book.