Florida here. I've had British Smarties plenty of times, because grocery stores in areas with large brit populations tend to have a good stock of British candy in the international food aisle. There's this one town in particular where a lot of wealthy Brits have Summer homes, and the Publix in that town is /full/ of the stuff. I've also had Aero, although it didn't stick out in my mind as anything but chocolate with holes in it. Can't say I've even heard of Coffee Crisp.
By the way, there /is/ a difference between Smarties and M&Ms other than the size: the shells on the Smarties are mildly flavored, M&Ms have food coloring but the shells are just sugar shells, no flavoring added.