The big question of this book is "exactly how much of it should have gone directly into the core?" At least two of the four chapters, certainly. You've got a group of people in the setting that mostly deal with spirits? They're going to need the spirit rules to do that. You've got a magic item background? People are going to want to know the benchmarks for using it (plus, you know, it's a little weird that this game about mages doesn't cover magical crafting by default.) When I look and see that the relevant sections are 26 pages total, I have to wonder - was Mage, Revised really so tightly packed, and if so, was it somehow impossible to add another chapter?
That's one of those economic and publishing industry questions that likely has a complex technical answer that is nonetheless completely unsatisfying.
The other half of the book is expanded setting information that's nice to have, would have improved the core were it included, but is fairly safely removable without noticeably hurting the core-only experience. It starts with a chapter about the history of the Awakened that mostly sums up the metaplot so far. It doesn't explain all the old canon (how the hell could it), but more or less gets you up to speed, assuming you don't care about all the weird legacy stuff that lurked in 2e's corners. The neater and tidier approach is, however, satisfying in its own way, allowing for a more distilled Mage experience.
The only really interesting thing is that canon is still playing it coy about whether Copernicus actually moved the entire Earth with the heliocentric theory. "It remains a hotly debated axis of metaphysical study." I like this particular bit of worldbuilding because it's so weird and so unnecessary, but it also sort of defines Mage by indicating that almost anything about reality is up for grabs.
We also see the Technocracy at its most realistically villainous in the second chapter. It's a recap and update of the Crafts from Book of Crafts, and since most of them are based off of non-European cultures, almost all of them have some version of "The Technocracy killed our members under the guise of European colonialism coming in and taking over our lands." It's not necessarily the most grotesquely brutal the Technocracy's been so far, but it is a repeated reminder that these guys are coming in and murdering people for what amounts to some pretty flimsy motives.
The ultimate (as in "last," but also the most affecting) example comes in the Wonders section, where it describes an item made by hippy mage, Poppy Jenkins. She had a magical string of love beads and it just blandly states that the beads were scattered when the Technocracy killed her. Just a callous little detail. They murdered her and they didn't even care about her prized possession. It feels real to me, in a way that the sci-fi horror rarely did.
But moving away from the villains of the Crafts chapter, I have to say that this is yet another case of White Wolf attempting to do through metaplot something they should have done with a retcon. In Revised edition, the Crafts are on the ropes. They're either hunted to near extinction or they've taken shelter with one of the larger Traditions.
The motives for this are completely transparent - a desire to change the fundamental design philosophy behind the Traditions. They are no longer vague rpg-class archetypes, but actually coalitions of specific cultural beliefs about the supernatural that happen to work well enough together to be a political bloc. I,e. Traditions are now supposed to be associations of Crafts. So you can't exactly have the old Crafts just floating around out there being all miscellaneous and out-traditioning the Traditions. Since Traditions are now supposed to be marriages of convenience, you can now just slot the Crafts into the most convenient Traditions.
It would have worked if the setting had been designed from the ground up with that in mind, but to make it a metaplot event is just weird. The Wu Lung are part of the Akashic Brotherhood now? Despite the fact that they are quite famously and emblematically enemies? Kind of sounds like you want a generic East Asian Tradition. With a bit more thought and the freedom to act, they could have been slotted into a more compatible Tradition from the very start.
Still, it was nice to see the old gang again, even if they're in much reduced circumstances. It's probably not a coincidence, though, that the best part of the chapter is the newcomers, the Taftani. I'm not going to go too much into them, because they get half a book later, but they're pagan Arabic fairy tale sorcerers who bind genies and give approximately zero shits about keeping a low profile, and they would be Mage: the Ascension's greatest invention were it not for the fact that the books like to pretend the World of Darkness keeps looking vaguely like Earth.
In the end, though, what I most wish had made it from the Storyteller's Companion to the Core is the clearer expression of Mage's fantasy genre. You can meet an abominable snowman. There's a goddess walking the Earth who was shattered into eight avatars and they're sending their minions to create identical temples so that her divided senses can feel whole. There are mysterious magical heirlooms and a healing wand that's powered by the imprisoned soul of a demon. I'm on the record as liking (maybe even preferring) Revised's more grounded tone, but it absolutely needs some of that fantasy whimsy to make it Mage.
Ukss Contribution:I'm going to have to go with poor Poppy's love beads. When you pick one up, fate conspires to have another fall into the hands of your true love. Then, as the beads call to each other, you two will meet and instantly have something to talk about. A dead hippy matchmaking from beyond the grave, using good vibes to reassemble her signature magical wonder. It's pretty cool.