the s3 intercooler is good for 500 bhp, therefore ths and forge twintercooler are not needed.
the forge is, however, easier to fit onto you oem cooler so will save you on labour time over the s3 and of course is easier to take off and sell on if you want to put your car back to standard.
am sure the ths kit is great but worth the money over the s3? no.