"The Off-Worlders" is a 1966 science-fiction novel by John Baxter, a prolific author who would later move to predominantly non-fiction, especially tour guides to Paris. It was his first novel published, and it was the other half of an Ace Double, along with The Star Magicians by Lin Carter.
There is a lot going on here. The first chapter introduces us to a character named "Elton Penn", who is studying in the London of the 29th century. After being introduced to him for a chapter, we then change the action to one David Boynton, who lives on a far-flung colony world, with his cousins, where the people practice Satanism and also technology is evil. But there are also Christians, apparently, who meet for secret orgies/raves, and the woman David is keen on, Samantha, is a Christian. But David is just a poor farm boy in a repressed region, until he meets a wounded man with a pet ferret who tells him there is a matter transmitter hidden in an old farmhouse. And when the mysterious man with a ferret dies, David and Samantha flee across their primitive world on foot, trying to discover why mysterious forces want to seize forbidden technology.
This story is not new: although it was a decade early, notice that at least some of these main points are basically Star Wars: Farm boy on a distant colony world being raised by extended family, is targeted by evil forces and has to seek help from an ancient religion. Much of the book's middle section, with an extended chase scene, followed by a scene where the villain gets the heroes alone in his office and reveals his master plan (before they escape), are standard suspense scenes, and don't add much to the book conceptually. The final few pages of the book, revealing the nature of the sufficiently advanced technology in question is interesting, and manages to raise some interesting philosophical questions.
As with many Ace Doubles, I feel that this book suffered from the editor's knife. There are some attempts at interesting sociological or philosophical points, there are interesting characters introduced (such as the ferret guy, and we never really learn why he has ferrets), but those parts seem to have been trimmed down or left without context, in favor of many mediocre chase scenes. For me, this was a good effort, but it didn't quite work.