I am guessing (based on my own experience with an iDJ Pro) that Numark uses switching power supplies that determine the input voltage levels themselves. My power adapter actually came with a clip-on bit where the socket prongs are, so they can be exchanged to fit european variations, us or uk for example.
Worst case is you might have to order a UK power adapter thru spares. Question then is does the discount of getting it in the US outweigh the cost of the extra adapter. But again, I do think the same adapter should work in both US and UK.
No doubt someone on here with a MixTrack Pro can have a quick look at his/her power adapter and tell you.
Other than that I don’t think there is much difference between a US and a UK model. Some brands (like Denon for instance) might include different software depending on the region (Denon has VDJ LE with the MC6000 in the US I believe and Traktor LE in Europe).
Greetinx,
Chuck