So I had the H&R 25mm lowering springs fitted to my 2012 S3 approx 12 months ago as well as tracking and 4 Wheel Alignment (a must if you change the springs).
Looks wise really happy, looks much better lowered. You can easily catch the bottom front lip/bumper on high kerbs and high speed bumps though so be warned - is fine for most but I do occasionally hear a scrape, you can't see it unless you get under the car though.
Cornering and handling wise it's a definite improvement and results in less body roll than I used to get under high speed cornering.
In terms of ride it is a little harsh over bumps, it's not what I'd call comfy at all unless the road is super smooth. I don't notice it so much as I'm used to it now but passengers do comment on it and my girlfriend isn't impressed on bumpy roads. Motorways are generally fine. I can't really remember what it felt like before they were fitted but it did feel smoother before I think.
I'm still running the stock dampers which I think is the problem. I'm only on 34k miles on the car in total and the guys I spoke to at AKS tuning said it would be fine for the H&R springs on the stock dampers on this mileage/age, but if you've got alot more miles on yours the dampers will probably result in an even more crashy experience. I think in the future I will get a set of Billstein B9s and a new set of H&R springs which would hopefully give a smoother driving experience while retaining the handling but not sure if I'd need a new Anti Lift Kit and Anti Roll Bars. I've held off on these out of fear it would make the ride even less comfortable than it already is as it's a daily car and I don't do track days as of yet so don't need racecar handling.