I have the one one welly fitted in my car S3. its F1 from the states.
A little bit chatter at idle, the engine revs a lot more freely.
Make sure if you go for a spring loaded clutch you get the right one.
I had one made and it turned into a nightmare, the made it wrong and i had the box off 3 times.
Less engine braking aswell, takes a little while to get used to, but well worth it imho