I have never heard them in person only on you-tube. Are they really loud? I have just the udder at the moment and its a bit too much. The 2 valves always sound better anyway but I still think they will be great on an S4R.
I have them on my 2007 S4Rs and they sound perfect I think. They are loud, but it's a good loud. They will be only slightly quieter than running with just the udder, however it is much less tinny sounding. You get a great roar without losing that Duc purr. Plus, they look amazing.
Also, motocreations has different options for baffles so you can quiet it down or make it louder. I went with the standard baffles. Talk to them, they are very helpful.
Thoughts - The sound is IMO perfect. I asked Mark from Motocreations to make them about the same volume as the unbaffled Termis. He said that it would be the quietest set he had made and that they would be a bit more restricted than the regular set-up but he would give it a go and that if I was not happy he would redo the baffles for me. The sound is slightly louder than the Termis but only slightly and a lot quieter than the udder set up I was running so I am very happy with it. The build quality is superb and I fitted them on my own in about 2 hours (most of that time was in getting the old header off the rear cylinder). I think the performance is unchanged. I'll get the bike properly tuned in the next week or so but it feels about the same. I like my bikes on the loud side but not ridiculous and this is just right.
I went for a quick ride yesterday and stopped at a local bike hangout. The pipes got a lot of attention!