This review is coming from a long-time PFS player, who was maybe hoping this book would be as good or better than the last two PFS-centric books before it: Pathfinder Society Field Guide and Seeker of Secrets.
What is in the book:
Front Inside Cover: Map of the Inner Sea region with all the Pathfinder Lodges marked, and whether they are active or not. I love this map, presents something I have always wondered and makes me want to know more about each lodge. Sadly, the book only ever expands on 6 lodges specifically in the book later.
Two-Page Spread: This is where those 6 lodges are expanded upon. Not bad, but I was really hoping for more. Wanted a bit more info on how the VCs got to their station, or more lodge back story.
Back Inside Cover: This seems totally out of place for this book. Methods of travel as a full-page spread? Who doesn't know this stuff? There are only two that are related to the PFS anyway.
Welcome to the Pathfinder Society: Neat information on these pages, but nothing that is not covered in the previous two books. Rehash.
Building a Pathfinder: Some interesting tidbits about generating a Pathfinder... but no crunch to go with the fluff. I actually think the Shattered Star Player's Guide is a better resource for how to build a Pathfinder, with some traits and such to go with it. the item kits here are not new. The sidebar here is allright, but generic.
Joining the Pathfinder Society: Allright! Finally something new! Here we talk about the two main ways to join the society, and with some crunch to go along with it. Sadly, the feats presented here I would never personally take, as they seem quite niche or lowpowered. Still, some flavor characters may benefit.
Scrolls, Spells, Swords: These three sections are about the crunchiest of the guide, with 3 feats, two traits and two spell each. I like the depictions of the glyph of the open road for each "groups", but I once again find the character options quite lacking. There are maybe two good feats, one which requires 12 ranks in a skill, which for PFS (the OP campaign) characters is pretty much unattainable. Some traits (like Clever Wordplay) are neat.
Pathfinder Field Agent: New (yay) Pretige class, also lacking any luster (aww). I will give it to the authors that it is thematic and pretty good flavor, but I would never want to play one. It is really a "super generelist" class, allowing you to pick what you want to advance every other level. Options include adding sneak attack dice, or getting a rogue talent, or getting wild empathy... basically a mix-and-match deal where you can add in things of multiple classes. I think the price is too high though.
Wayfinders: Section with new ones. I like this section, as it is all new stuff. My only gripe here is again, looking at this book from the perspective of a PFS OP campaign player, there are a bunch in here than are un-purchasable. Three of the seven wayfinders cost 39,000 gold or more...
Ioun Stones: I was super excited when they said new ioun stones were going to be covered in this book. Seeker of Secrets was an excellent source of info on the stones. The Primer adds 7 new ones, along with their cracked and flawed counterparts, and resonant powers. But like the crunch above I was a bit underwhelmed. A few are pretty neat, but otherwise they are quite dull and/or too pricey.
Magic Items: All-crunch section. Liked the new items. Some are actually both useful and affordable. lenses of situational sight are actually quite good.
Pathfinder Chronicles and Vanities: The next two sections I actually like a lot, providing both good fluff and some good options for characters. Some of the vanities especially are quite neat, and honestly, you can never have too many vanity options.
PFSOP: Two pages of pure marketing material for the OP campaign. Doesn't bother me that much, but with such a PFS centric book, I'd think most readers are already familiar.
Conclusion
I wanted to like this book, I really did. Maybe I came in with too high of expectations. But I barely found anything useful. Out of the fluff chapters, only the section about the two ways to get into the society felt fresh. Everything else felt like a reprint of either the Field Guide or Seeker of Secrets.
For the crunch, there was a lot of it which was geared towards more flavor characters, which I don't build often. I honestly felt like 95% of the feats, spells, traits and magic items were very low powered. It seemed like the authors were "holding back" on the power level on purpose due to the fact that the book is expected to become completely legal for the PFS OP campaign, so they wanted to make sure nothing was broken. I think it was dialed back a bit too much.
For now, I will keep to the Field Guide and Seeker of Secrets when someone asks for a recommendation on what to get for the PFS OP campaign.