I Have one on my GSXR1000 trackbike. It just allows me to keep the throttle nauled on the straights and sometimes allows me to change up exiting fast sweeping bends without undue movement from my upper body.
Not having one on an NSR it is hard for me to comment on the use on a two stroke but i'm sure some of the racers here Chester, Fontyy etc will give you more info.
Dependant on the type you get will depend on how hard it is to set up. They are rarely plug and play and a badly set up quick shifter could make you slower.