Content warning Spoilers for halfway through and ending!
Written when I was about halfway through the book: So there's this thing the author is doing where he's trying to imply that the Joins are a marginalized class because of the ignorance and bigotry of Solos, and it's so clearly a non-marginalized person's understanding of marginalization it's getting a bit uncomfortable to read. Becoming a Join has a high financial cost that's discussed multiple times throughout the book, as well as having intense psychological and physical evaluation requirements and being entirely at the mercy of someone choosing to Join with you. And you're also putting yourself in the hands of the large corporation/government's very specific laws pertaining to Joins and Joining procedures and tracking. Many Solos are also demonstrably living in reduced circumstances, in slums and poverty (the main characters literally go to the slums to check out Solo-only bars, because that's the one place you'll find them), with far fewer and more dangerous job opportunities (Solos are unable to pilot cargo aircraft for example, or Pod technology, they're left using antiquated personal vehicles and driving surface cargo despite mega storms that make this incredibly dangerous. All other technologies seem to have developed alongside Join, leaving Solos using outdated tech for everything from transportation to housing and communication). Yet being a Solo is repeatedly treated as some choice that demonstrates a bigotry towards and misunderstanding of Joins, and conversations where Solos discuss their upset about these circumstances (e.g., the alto sax player who bemoans the fact the Solos are basically locked out of creative careers like music) are treated like micro aggressions against the Join main characters. Despite the similarities to Sens8, this isn't a genetic condition that people develop at birth, it's literally a technology attainable only by the extremely privileged.
Written when I finished it: Join redeemed itself slightly from my earlier assessment, but not in a very satisfying way. The main character(s) have a change of heart without almost no sign and very little motivation, and end up sacrificing a great deal to sabotage the ambitions of the company/government and the Joins, in order to redirect their attention to saving the Earth. Though it also ends with the company/government making joining so cheap and accessible that the goal is basically to eradicate Solos, so I dunno.
Overall, it was an interesting premise? And I kept imagining all the characters with 80s/90s clothing and hairstyles based on the descriptions? But it felt more like a thought experiment than a coherent narrative.