ta - is there no cheaper option ?! Does it just clamp onto the end ?
The official tip has a cut out at the top to fit the down section of the exhaust exit. You will struggle to find a cheaper non-AR tip to fit. 2nd hand, (try fleabay) is probably your best bet if you don't want to shell out brand new prices.
Very tempting... Just spent £70 on an iPod adapter (saved £108 by fitting it myself) so can't splash out just yet, but definitely adding this to my to-do list, alongside getting the horse shoe alloys..