The quest for button controls on iOS that don't suck is an unending one. Touchscreen buttons suck, and the hardware out that works with the iOS controller API so far is fine, but it's big and sort of annoyingly deliberate. Razer's Junglecat, though, is a solution that feels right.
The Junglecat's advantage is in its slickness. Instead of bolting onto the sides of your iPhone, it's a slider case that harkens back to the old, hardware keyboard days. Except instead of QWERTY, you've got a joystick and some buttons. And at a pretty small cost when it comes to added girth.
To pull this off though, the Junglecat does have to make a few concessions. It's not a dual joystick joing, instead opting for a more old-school SNES approach. It also doesn't pack any battery of its own, so extended gaming sessions will drain your battery as fast as they would normally, maybe faster.
But the Junglecat's biggest advantage is that it's convenient. Like a camera, the best controller is the one you have with you. And in this compact case form, you can have a controller with you all the time without needing a whole other pocket to store it in. A controller that you don't have to remember to bring with you.
Whether that connivence is worth the $100 that a Junglecat costs is another question. But it's promising to see a company with a pedigree like Razer take on the challenge in a way that's equally subtle and awesome. Playing emulated Gameboy games on the train is about to get way better.