ANCC novice champion navigator in my first year. Did it for 15 years.
I'm no fan of Quaife and I've had to work with them a couple of times, but the range of suppliers is limited. I'm running an Mfactory in my 02J. Keep an eye on the website as they have sales. Mine cost under £500. I've got a Gripper in a MK1 Golf which is definitely the more fun device but needs more maintenance.
You will find the small wheel arches limit tyre choice and the lower height of the GTi is not ideal.