steve, the euro head units do use different frequencies, the US frequencies are limites to odd tenths of a Mhz: e.g. 97.1 97.3 97.5. European head units can go into both odd and even frequencies.
So, the euro ones should work fine in the states cos they can tune into both odd and even frequencies. So dont rule them out, they will work fine if u are prepared to filter through the even tenths.