Variator Springs are a sensible purchase when tuning a scooter.
Why? Powerful Engines can cause the Belt to slip. A reinforced Variator Spring presses more strongly on the rear half of the pulley and thus increases the contact pressure - the Belt is better "wrapped" and slips less. In this respect, engine tuning without a Reinforced Variator Spring makes about as much sense as skiing in the Netherlands.
OEM numbers (for comparisons):
243.040 - ap (POLINI)