This controller by rotor riot is the first to support the L3 and R3 buttons that have been missing from the MFi standard for so long. The company is actually run by drone enthusiasts that decided to build a controller to reliably control their drones with tactile feedback. It is also one of the few controllers that doesn't rely on it's own battery but directly attaches to your iOS device via lightning port and draws power from there. That can be a plus but also a drawback. It's been rumored that Apple will change the port from lightning to USB-C, that might make this controller obsolete in the coming months.