on a 3door, you use the std light anyway so pointless getting one.

for a saph etc. it does come in handy as it saves a lot of feckin about with LEDs and bits of wire otherwise...

they're not NEEDED to read out fault codes etc, its just a hell of a ot easier to do it wth one, so for the sake of a tenner worth getting

also buy the one for the EARLY model cars even if you wanna use it on a later model, as the early one fits all sockets (inc later ones )