First, I had no idea this book was based on a British radio show ... perhaps that would make a difference, but since the number of potential readers who are familiar with the show is probably a very low percentage, I don't know that it matters that much.
Second, a book's style and genre create certain expectations (or perhaps in this case "xpectations"). A funny book, which this often is, that is clearly outrageous fantasy, which this book always is, generates a certain mood in the reader. Also, science fiction and fantasy novels almost always "conclude," in the sense that the plot and issues raised during the book are resolved in some satisfactory manner.
"The Quanderhorn Xperimentations" fails on that score, rather dramatically, ending with a thud that makes you re-read the final pages, hoping you missed something -- but you didn't.
On top of that, the bulk of the book is the repetition of essentially the same jokes about the protagonists. One member, for example, is terminally stupid; another is a cowardly liar; and so on, and after a while the laugh track runs very thin. (Now maybe in a weekly radio broadcast, the jokes would seem fresher. Not, however, in a book unless you only pick it up once a week.)
So in short, don't buy this book, and don't invest any time in reading it even if someone gives it to you. I've reviewed a lot of books, and one-star ratings are very rare -- but "The Quanderhorn Xperimentations" sank to that level on merit, plain and simple.