The gen 3 is a piggy-back efi controller because it does not replace the stock ecu, but rather monitors the signals to the injectors and makes fuel adjustments based on the mode settings.The gen 3 has a push button interface allowing access up to 6 different modes to allow for quick fine tuning by the end user without needing a computer.The gen 3 also is nitrous oxide compatible, and allows the user to add fuel thru the stock fuel injection when using nitrous oxide.