Speaking from experience – a head unit from North America will not get good FM radio reception in Europe. This is due to differencies in frequency steppings. If i remember correctly my US head unit only locked on odd numbers (99.1, 99.3, 99.5 and so on) so when I wanted to tune in to stations on even numbers (like 99.2 MHz) the best I would get is bad reception and many times I’d get no reception at all.
edit: The head unit will of course tune in to stations on odd frequencies without a problem.