I am giving this book 5 stars not because I liked it, but because it has significantly improved my scholarship --- at least, in the last few days since I started reading it. We'll see if it continues!
The crux of the book is "write down insights you have, as you're having them, and then regularly reconcile these into a single place, and track insights you have while writing THOSE down. Rinse and repeat." It's been a very helpful framework for thinking about big thoughts; rather than trying to keep it all jumbled up in your head, or rather than trying to serialize it into a coherent piece of prose, just write down the idea. You can shape it later. It's an excellent tool for decomposing hard problems that require lots of moving machinery to get your mind around. When you're actively searching for, and reveling in insights, learning becomes fun, and spending time doing scholarship becomes the norm. Life pro tip.
The only other good thing I'll say about this book is that it's short. I got through it in two sittings. Really and truly, the only content here is that thing I said above. Have ideas and write them down. The rest of this book is a bunch of bad pop-sci that is sorta tangentially related. I get the impression that Ahrens was Taking Smart Notes on all of the bad pop-sci books he read, and couldn't help but write about them here as filler. The useful part of this book could be a blog post, but you can't sell a blog post!
Unrelatedly, I feel like I've read all the same bad pop-sci books as Ahrens. I'm not sure if this a failure on his part, or on mine :(
I'll begrudgingly recommend this as an excellent book I've read this year, if just for its information content, and not for the book itself. Feel free to skip any paragraph whose first sentence doesn't mention a slip-box; you won't miss much.