Pinlo's last case, Slice, rode the fine edge between intriguing and not-so-hot due to a very aggressively thin design that felt almost like wrapping the glass iPhone 4 in paper. The company's latest offering, United ($33), is edgy for different reasons: it's the very rare iPhone case to use metal in its frame, combining one piece of machined rear aluminum with your choice of two differently-colored plastic front shells, one clear and the other either…
