I love the idea, being a detailer, I have to put the cap on top of the flap. I'm not a fan of that because of it touching the paint.
I suppose I could cut the tether but then I'd drive off without it. The idea is great but it would have to be fully certified for use in the uk. It's a biggie ain't it a fuel cap.
Another thing to consider is if it would work with our v power pumps. I've found recently that all of shell v power pump nozzles are different from standard diesel nozzles. Different enough for new bmws not to like them. I can hardly ever put v power diesel in my old mans car, the pump just clicks and cuts off.
I would hope that this cap won't cause anything like that.
Sorry for the waffling!