To more clearly explain this, here's the description from Oliver's website: "Replica is a “flip book” that contains two narratives in one. Turn the book one way and read Lyra’s story; turn the book over and upside down and read Gemma’s story. The stories can be read separately, one after the other, or in alternating chapters."
Though I'm always complaining about books with point-of-view switches, I chose to keep going back and forth between Lyra and Gemma's stories. Oddly enough, I thought that worked very well, especially when you consider that after reading a chapter from one character's point-of-view, I'd often read another chapter covering the same material, but from the other character's point-of-view. My complaint about point-of-view switches is that I feel they slow narrative drive. I didn't feel that was the case here, even though you'd think that covering the same material twice would do just that.