I am a fan of Colfer's work. His fantasies can appeal to almost any reader because they have an added layer of irony about the entire genre. Benny and Babe isn't a fantasy, rather realistic fiction set in contemporary Ireland. Overall I give this a very positive review--it addresses issues of male/female adolescent friendships, bullying, and general adolescent issues. Unfortunately for American readers there is also a lot of regional background knowledge assumed. It may be a good book to help students learn to read over cultural information they don't understand to get to the good "bits" of a book. It's a skill they can use in reading fiction that is written in unfamiliar registers (Swift, Shakespeare, Wharton, etc.). But, it probably isn't going to become a classic book or one included in the "canon" so I'd only recommend using it with students who are Colfer aficionados. Those students will need a bit of introduction to the book and a strategy for reading over the unfamiliar bits in the first chapter, "Culchie Hurling."
Having spent a lot of time on Puget Sound I enjoyed the setting of the book, a seashore town, and the fishing adventures of Benny and Babe . Readers from desert climates may not have the feel of the setting, but the stories of adolescent adventures and attempts to make some spending money through summer vacation may carry them through the book. Those who live in or have visited resort communities will appreciate the tensions between the townies and the vacationers. The life threatening adventure near the end of the book will grab almost any reader, but especial those who live or have visited the Pacific Coast of the US.
I doubt this book will have a wide readership because of the regional idiosyncrasies, but it is one I will recommend to a few selected readers ready for its challenges.