The only problem is that those top-up cards, as they are known, might be hard-locked to the EU region. Those gift cards tend to be region specific. I don't mean to spam but maybe European cards don't work in Cincinnati so to speak. Don't spend more than you can afford to immediately lose abroad. These Americans need a dictionary for everything, and that's why we love them. Imagine if the British imperial loss over in USA, was a British intelligence job. Owning you for decades you poor Americans.

Edit: typo Fixed