Nubian - I actually don't (I'm perfectly happy with my single rating at the moment) but I was just intrigued by the number of people telling me different things about the validity of the 61.75 FAA license.
In particular the strongly asserted opinions of those that certainly should know the rules but who, it turns out, don't.
That said, if at some unlikely point someone kindly offers me the opportunity to fly their N reg MD500 I'd seriously consider doing the requisite conversion training and the paperwork to get my 61.75 FAA license to be able to do so, rather than spending the time and money to get and then maintain the separate rating via the conventional EASA route. As I said above, I understand a significant number of pilots are already doing this - I just couldn't find the confirmation of how this worked. All credit to Gordy for having done so.