I have, albeit on the 911.
Why do you want one? If it's to hopefully get your car back after it's been stolen, then go for it. If it's for any other reason (insurance et al) then I wouldn't bother. £225 does seem very cheap for that (Tracker themselves say £462), but don't forget the annual subscription of £174. For me, that's a cost just too high for a car that's not known for being stolen. The Tracker Cat5 Plus looks similar to the Cobra system I use, as you get a keycard that must be with the vehicle when you're driving, and in theory offers a much better chance of recovery as you'll know exactly when your car has been stolen (they call or text you). More expensive though, for obvious reasons.