OK, no experience but I did some research and, from what I can see you are correct. The only advantage it gives is a small "environmentally friendly" effect. The downside is excessively hot gasses in the pipes that will badly discolour them, rough running and excessive "popping" on deceleration. So it all depends. Are you a tree hugger? Im guessing not. So get that rubbish off.
The next problem is that, from my quick research, later models (from 2008 up?) are more complicated to "fix" than the earlier ones. Not having worked on either an early or late one, I cant tell you how hard or how much harder it is.
Cheers Bloke, green I ain't, and thanks TC, had a look at the rat site, looks pretty straightforward. Skimming through some of the posts, I thought there's some right dimmos on yer, then saw where most of them were from.
The power of ARRSE is wonderous indeed. I shall proceed post haste. Thanks again.