The Watchtowers and their surrounding Supernal Realms are the most interesting part of the book, and, indeed, one of the most interesting things in Mage: the Awakening's setting, but you can never go there. Once upon a time, perhaps during session zero, maybe as late as the first half of session one, your character had a dream about a magical realm, where they overcame fantastic hazards to enter a wondrous structure, to write their name on the walls and thereby make peace with the realm, earning the power to work magic. And that's all your path is, the memory of that dream.
The conceit of this book is that the paths have other implications, that they each represent a particular world-view and color how your character works their magic, but honestly, those implications have yet to be interesting enough to justify their existence. What it amounts to in play is some xp discounts that might influence your choice of Arcana and a bunch of superficial differences to the same basic magic system. Is your wand made of iron or gold? When you regain mana at a Hallow, do you meditate about death or do you meditate about your place in the cosmic hierarchy? Is your signature fragrance cedar or musk (oh, yeah, the paths each get their own signature fragrance)?
In the end, though, the Paths kind of come across as akin to something like D&D's alignment or an astrological sign. You can say, in-setting, that you're an Acanthus, just like you can say in the real world that you're a Capricorn, and that's a meaningful statement, but politically and socially, you're going to be part of an Order and a Concillium and a Cabal, none of which even care what path you are, and maybe you have things in common with your path-mates, but the paths don't have an organization or an agenda. They exist as an origin story for your magic . . . except that the different origins aren't really a place. Maybe there's an Arcadia. Maybe there's a Pandemonium. Lots of different people have dreams about them, and those dreams grant similar types of magic to similar types of people, but you're never going to see those faeries again. You don't have to worry about the demons catching up to you.
And that, I think, is a fatal flaw, not just of Tome of the Watchtowers, but of Mage: the Awakening as a whole. The Supernal Realms are interesting places, but they're not used as places. They're at best a set of symbols that may, with effort, show up in the game as part of its theme and mood (and let me tell you, the existence of five different "theme" and "mood" sections in such close proximity did little to alleviate my grumpiness with this book). It's exactly backwards. Angels and infinite jungles and a waystation between life and death - those are elements that help build a memorable fantasy setting. Ideas like "triumph over adversity" or "respectful contemplation" are subordinate to characters, setting, and plot. Yes, if you want to make something with artistic merit, you have to ask literary questions, but no one is going to give a shit about the answers if the overall work is boring.
Mage: the Awakening has these Supernal Realms inspired by high fantasy, but it aims at being an urban fantasy story set in a world of covert magic. So it confines the Realms to the game's temporal book-ends. Your path is your origin story, established in session zero, but it's also your endgame. The idea of bridging the Abyss and returning to the Supernal world is teased as a long-term project, but it's also something that's definitely not going to happen within the scope of the game. If Ascension is possible, it is functionally indistinguishable from death. Therefor it can only happen at the very end of the story. Your path may matter in the epilogue, just as it did in the prologue, but for the time in the middle, it's merely a set of symbols. Sometimes foreshadowing, sometimes a flashback, but never an actual event, described in literal terms, happening in the here and now.
Tome of the Watchtowers never quite overcomes this limitation. Fundamentally, it's about nothing. Your character's star sign in a world where astrology really works, but that's as far as it goes. It's not an entirely useless book. It gives suggestions about character concepts, magical nimbuses, the sanctum background, and ways to reskin the basic oblation ritual, and these suggestions may help you create and portray a more fleshed-out character. However, whatever use you do get out of it is likely to be exhausted prior to session zero. The Watchtowers work better as fantasy than as mysticism, but unfortunately they're in a game that would rather do half-assed mysticism than solid fantasy.
Ukss Contribution: But while we're on the subject of fantasy, one of the suggested nimbuses makes people grow hair. I like that. It's weird, it's creepy, it's invasive - not quite body horror, but also not not body horror. And most importantly, it's a real effect. The people who witness your magic are actually growing hair, and it's not an illusion or a dream, but something that endures. If you want to get rid of it, you have to cut it off. I like it. It's a nice change of pace in a game with a Disbelief mechanic that exists only to make sure that its magic doesn't have too permanent an impact on the physical world.