Just had mine done today. Some background: 2013 S4, build date August 2012.... picked up October 2012.
I had the slip issue, but mildly from day one. Alu Kreuz helped a lot from the beginning.
Many debunk the theory that AK can help the sloppy steering, but it does make a difference.

Never had the notchy issue until about 2 weeks ago at 4,400 miles. Only when starting the car in the morning and goes away within a few minutes.
Never disabled DSR and never had the rack replaced.
I expected more from the update. I'm sensing only a slight overall improvement. Better on center feel and slightly less correction needed
to keep the car straight. Slightly heavier feel at the wheel but was hoping for MUCH firmer resistance. No such luck.....

I'd guess that if you had the slip/notchy issue much more severely and your steering can get to the way mine feels, you'll be very pleased
with the update.

Why am I not convinced that this is the ultimate fix? I wonder now if disabling DSR would make more of a difference.
SA said this update should fix the slip and notchy issue..... not convinced they know the truth about that either.
Will see over the next few days if the notchy feeling at start up is gone.....