Depends on how you see it. I see this as completing the car if you go down the handling route. The little difference it makes is confidence in the 4wd system mid corner. I had a little play the other night in attack mode on a corner I know very well, I managed a small 4 wheel drift in my S3, where it would usually go into understeer on the exit of the corner. I have no doubt the Haldex performance controller did it's job there, but you need to be committed to get into this position in the first place!
I don't expect everyone's driving style to be the same, but you really need an open space like a track day to get to know your car a bit better to make the most of this bit of equipment.