As someone who loves both worldbuilding and is also a systems/mechanics nerd, I really enjoyed how this was designed structured and implemented and as a DM, I can see myself using it for years into the future, if for nothing else than just inspiration for features to put into various towns and settlements, regardless of the mechanical structure behind them.
I would however caution against the author's suggestion that this book can be used seamlessly with Colville's Strongholds and Followers. It can't really without greatly increasing the DM workload, beyond the increase in workload I already volunteered for when I decided I wanted to give my players stronghold and settlement mechanics to play with.
The system breaks down with units and mass combat, this supplement uses a system whereby a unit's mechanics/stats are derived from the settlement they come from and work under the assumption of fast resolution in combat, with a single competing d20 roll deciding the outcome. Contrast this with the system presented in S&F where unit mechanics and statistics are inherent to the unit and not irrevocably tied to the stronghold they come from, and are designed for a more engaged back and forth with other enemy units. Could you extrapolate back and forth? Kind of, but at the end of it you would be running two competing rulessets for the exact same in-game circumstance.
That's not a criticism against this book, however, so much as a note to take one specific claim made by the author in an info-blurb with a grain of salt, because the Author does oversell the compatibility of the systems. The venn diagrams definitely overlap, and they overlap in such a way that means you have to fundamentally change either this rulesset or S&Fs in order to get them to play nicely together.
This book, however, would be worth its full price tag, even if you never once directly implemented any of the mechanical underpinnings in game. The potential of this book as a worldbuilding tool to create flushed out, well rounded settlements quickly is unparalleled.
You could start by following the rules for building a settlement, starting with how big you want your end settlement to be, following the building prerequisite rules, as though you were going to use the mechancis presented in this supplement, and then, once you're done, set aside the statistics and what you're left with is a detailed description of a settlement, the people who live there, even the minority populations that might live there, and a listing of all of the points of interest inside of that settlement that are unique to that settlement's structure and needs, and you've done it in about 15-20 minutes once you know the system.
To go from a single-line premise like "industrial mining city" to knowing every one of the potential points of interest your players might explore there in 20 minutes is chef's kiss.
Amazing supplement, worth every penny, 5/5 and the author got a little ahead of themselves on a single blurb on a single page towards the front of the book.
[5 of 5 Stars!]