The only other thing I would add is that I'm not entirely sure if the US 240V 60Hz peak voltage would be within the safe limits for a 230V 50Hz European appliance.
Do you know what the normal voltage range one would expect to see at a US 240V outlet is ?
If it's a simple coffee pot without any electronics on board, it will be unlikely to know the difference. However, if it's a modern espresso machine or anything with a lot of electronics on board the US supply might fry its electronics or at least reduce their life span substantially.
I know I have heard some weird problems where people have installed European washing machines on US 240V supplies i.e. electronics have malfunctioned. There can be quite a surprising amount of electronics in modern Euro washing machines not only the cycle controls but also solid state controls for variable speed drives which may be quite sensitive to not getting exactly their rated voltage and frequency.
I'd say if its a simple coffee pot though, you've very little that can go wrong
