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.
Edit: there is one British candy I've had that's straight up better than its American equivalent: the Mars Bar. The closest thing we have is Three Musketeers, and it's pretty good, but the Mars Bar has a thicker layer of higher quality chocolate. It's the same thing but better, basically. Aldi's store brand has a lot of stuff like this, too. You get better chocolate going into Aldi and buying the store brand in this country than you do buying fancy expensive chocolate, let alone the mass market stuff it's competing with. Let that sink in for a minute.