Not too harsh really.
They can be a bit noisey, but not something overly annoying, especially when you are considering the use of the vehicle. The grippers are pretty quiet...Sadevs are a bit noiser I find.
They also dont need regular maintenance. Plates on race cars I work with are changed in the order of years,....not regular put it that way.
As for the Quaiffe ATB, have you driven a clio with one fitted?
I have, couldnt tell difference from std at all. In fact, if I wasnt told it was there, I would have thought it was std.