This is a plug adaptor meaning if you have a plug with a certain shape, you use this to be able to plug into a wall plug with a different shape.
This is an adaptor to use with items like computers and phone chargers that work with range of voltage. And it works when the voltage of both the native country and the destination country are the same but the plug configuration is different which could include hair dryers or anything else.
This is not a transformer, that is, it does not convert from one voltage to another. For that you need a transformer. A good heavy duty transformer would weigh over two pounds and probably cost over $50. But even with a transformer it is difficult to use 'heating appliances such as hair dryers and irons on different voltage than they were designed for. But you can use this adaptor if your hairdryer already has a switch feature that allows it to be either 110 or 240.
It is difficult to use 'heating items' such as hair dryers and irons on different voltage than they were designed for. If your hairdryer already has a switch feature that allows it to be either 110 or 240 you may use this plug. Otherwise, plan to buy a hair dryer at your destination country.
It is just a plug adapter for many countries so I would say it would work in Greece. You still might need a step down transformer to step the voltage down from 240VAC to 120VAC. The Simran SMF-200 Deluxe 200 Watts Step Down Voltage Converter for International Travel to AC 220V/240V Countries, works well for that too.