i personally have the Radtec makes a great diffrence and do recoment but are pricey compared to some others i beleve the airtec is prob about the best value for money and people always have good coments about them
I have a black Airtec gen3 and its a great piece of kit considering what some can cost you. Easy to fit too, did mine in an hour and im no mechanic! Just make sure the boost pipes are nice and tight cause i got the old 'ESP System Failure' due to mine not being tight enough. You will notice a big dif when it gets abit warmer.
I also have the Airtec gen3, got it on the group buy for £250 - absolute bargain, you will really see the difference come summer. Great piece of kit, it looks really good in silver behind the grill. As Simo has said it beat the rest in magazine tests so it really is great choice. I know a few people missed out on the group buy, maybe you could speak to Alan @AS to organise another one? When May arrives everyone who hasnt got one will want one!