What is wrong with your arms? Can't move them quick enough?
Only joking... No, but seriously?
The short shifter makes the forward / backward throw a bit shorter. There is no performance benefit, no quicker shifting times, just less arm movement. So if that is something that is worth spending money on, sure do it.
I cut my gear selector shorter by a good 5cm in my 156 racer as my fixed racing seat is WAY lower than OEM seating position and the angle was awkward. Now it has shorter forward / backward AND shorter left / right throw. I am actually slower with gear selection at the moment as I have to think about it... with more practice I'll get quick again