Hi Phil
I am currently fitting the Freestyle super wide track set up to my S3, so I can't comment on the differences to handling yet but what i would say is that Gary May and his company have been great to deal with and i would not hesitate to recommend them.
The front end has been fairly simple to fit and other than sourcing the SV de dion tube and drive shafts the rear end is the same. I have chosen the Quantum shocks which are the next part of the build when they arrive.
The SV rear end means you need to budget for the wider wheel arches but gives you more options for wider wheels, 9" rears are no problem.