Here is their product:
http://shop.boyesen.com/catalog/prod...oducts_id=1023
When I bought my bike used, it had this system on it. Back then, they called it the "flex grip". Looks like they renamed it for marketing purposes. Look at the pic (see above link), it is the same system I had.
I can't comment on it reducing arm pump, since I really never had a issue with a normal bar setup. However, it does help reduce blisters on my hands since the grip flexed a bit. There are several different durometer bumpers included to control the amount of flex. Your really don't notice it rotating that much... maybe a couple degrees if that.
I ended up taking it off for two reasons:
First, the system requires you to get a special grip for under their barrel. You could buy their grips but I like to have more options. So, I ended up buying two sets of grips to get the throttle-size ID grips (one for the throttle and one for the flex/shok barrel). Then, you end up with a collection of standard left grips laying around.
Secondly, I did not like the feel of a larger barrel under my left hand. Since this is my dominate hand to hold the bike, the larger barrel would cause hand cramps. I prefer a small diameter to allow me to loosen my grip occassionally and reduce fatigue.
Conclusion:
It goes work for providing a controlled degree of rotation. This is useful for reducing blisters and/or wrist pain. However, this may or may not help reduce arm pump. I believe that diet, nutrition/hydration, and endurance are the best solution for arm pump. Since grips and bike ergonomics are very personalized, it's difficult to say if this is the best thing for most riders. For me, I found other drawbacks to their product which made me stop using it.