It does not change the voltage.

On their online shop they post a warning:
- Achtung: Dieser Adapter bewirkt keine Spannungswandlung! -

Using hair dryers or curling irons at twice the voltage is dangerous!

Pin adapters have somewhat flimsy internal contacts to make it possible to change the pins without to much force (or make the adapter to big) . The current should not exeed 2,5 amps (110V-275W, 220V-500W).
They are widely used in Europe, most countries have their own plugs, the voltage is always 220-240V

Rob