It seems strange to see a long article on the novelty of Frontback without mentioning that it mimics and seems largely inspired by the built-in Dual Shot feature on Galaxy S4.
Actually, it wasn't inspired. The first time I ever heard about the Dual Shot (sorry I don't pay enough attention to Samsung) was two weeks before we submitted to the App Store.
That's exactly why it's interesting. Out of a hardward feature on Galaxy S4 they made an iOS app.
Never heard of frontback, but wow! What a brilliantly simple idea. I told my younger sister about it, who loves Instagram, PicStitch, and all the other photography apps, and she could not have been more excited. I don't know if it will spread like the others, but I am very impressed by the idea.