Hi, I figured I'd bump the thread and answer your query, but maybe others would add their thoughts too?
Initially, I would of said they don't really quieten the road noise down by much, and their primary function was to stop folk peering into your boot.
But, I've got a K1, which is fairly noisy and recently, I had to remove my tonneau to carry something in the boot, it was then that I did notice a definite difference in the level of noise coming from the rear. I've also been told by members that their partners like the dividers as it quietens the exhaust noise
So, it would appear, that on average, 8 out of 10 cats said that it did reduce road and exhaust noise
Hope that helps