I have this on my bike now. It allows full action with only 75% of the grip rotation. I like that my arm/wrist no longer has to move as much as before.
What I noticed is that the grip is harder to rotate, which to a degree is natural since the throttle assembly is moved by a shorter twist.
If I wanted to smoothen it - where do I attack? Grease up the grip tube? Throttle bar assembly plastic box? Wire? Oil or grease?
I'd try the cable.