I've brought one from BigPhil and love it, sounds immense, at about 3,500rpm you get an almost whistling sound then over 4,000rpm and the engine just roars better than ever before!
It will hit your MPG though as you'll find that for first 3 months you'll drive keeping the revs high just hear it all going on!!
I'm not a mechanic by any stretch, never go under the bonnet other than to check engine fluid levels - but even I managed to fit it in under 45 mins, someone who knows what they're doing would do it 15mins
Enjoy