the only reason to get the kartboy weighted shift knob is just physics. you have the inertia of the weighted shift knob helping you put the car into gear because of the reduced arm of the short shifter. same force x smaller arm = smaller moment
to overcome this smaller moment, you can either use the same shift knob with a greater force, or you can use the weighted shift knob. the weighted shift knob requires a greater ammount of force to start moving, but adds its inertia to the force of your shift throw and you get a greater net force trying to stop the shift. you are using the same amount of force to put the car into gear, but it may seem less because the shorter throw isnt puting against your hand, its pushing against your hand and the weighted shift knob. i personally have a kart boy short shifter without the weighted shift knob, but i miss shifts just running around town when not trying to speed shift about once a month. its personal prefernce, but i like the non weighted shift knob. plus, on really hot or cold days, you hand isnt fried or frozen when you go to shift.