An aircraft with a fixed pitch propeller can be compaired with a one-gear-car - it is not efficient enough for short take off nor is it for fast cruise.
A VPP can reduce your take off roll and increase your cruise speed considerably. And it reduces your fuel consumption as a positive side effect.
You will be pleased about that on the gas station next time.
The Rospeller VPP is specifically made for Rotax engines with heir hollow gearshaft in order to control the propeller mechanically via a push pull rod through the gearshaft.
Of course the Rospeller VPP is also suitable for every other engine with a hollow gearshaft!