As mentioned Roverrons box of tricks takes 10 minutes to fit.I have one and a K+N on my wifes 02 TD4 and its like having a new car.
We had some issues recently with the performance which Ron sorted very quickly indeed and the car was awful as standard, when the new box went back on, the car felt fantastic again.
I have had lots of my cars re-mapped by specialists who claim the world in performance gains, some have felt good others not as much but based on cost and instant gains and i do mean you will instantly feel the difference Rons box of tricks cannot be beaten.