I know some people using them and I have them for exactly one year.
Hope yours don't have the splicing problem.
You run 255/40?
Grip in the dry isn't as good as with R888, but far better than with any
regular street tyre and as well as the Hankook R-S2.
I have no direct comparison with true semi slick in the wet, but the RS-R
is not as grippy in the wet as standard street like Conti or Pirelli P Zero.
So be careful in the wet. And yes - it's noisy.
ps:
mine (purchased in Germany) are road legal