Hi Hamish,
As tarbat rightly mentioned I have been running the Watson Radar Extender for since I got RB really. I am located in the NW of Ireland, no major 'airport' traffic to talk about except for 'Ireland West' AKA 'Knock'. I am approx 35 miles away and get them onto the ground.
With the RB antenna my max range was approx 165 miles, I see traffic now into Scotland as far as Inverness/Wales/IOM and of course all transatlantic flights coming over Ireland. Approx range now is 215 nm to the south of my location being cut right down to approx 70nm to the NW because of high mountain ranges.
I have the antenna connected to Westflex cable and it has a 15 meter run to the RB. The antenna is located on the gable of the house.
The antenna definitely works well for me and I am happy with the results. Hope this helps.