I haven’t a clue if they’ve done well here or not, I’m just guessing really as I have seen no more than 2 in all my travels around the country. I do know it got quite a critical reception here due to its cost and iPhone 8 marketing seems more prevalent in my experience.I'm sure there are other factors at play as well, but if you're in a place where most people just can't afford the iPhone X, then you're not going to see many of them.
I'm surprised they haven't done better in the UK. Around here, 7's and 8's are still far more prevalent, but given how many of those there are, I still see plenty of X's around. I also live in a relatively wealthy state, so that probably helps too. I can spot a X across the room now because of the notch, which was clearly part of the design....
None of my friends or associates have an X despite the iPhone being the dominant brand and affording it is not the issue. Perhaps it doesn’t quite have the appeal is does elsewhere?