And fondly hope that it works on my yet to buy Xbox S.
Done my homework now, and it appears UHDBDs, unlike DVDs and ordinary BDs aren't "zoned" so you should be able to play US UHDBDs on UK sourced players in the UK. I say should...
As for economics, a typical "blockbuster" is about $25, which, at the current 77 pence to the Dollar, is about GBP19.25.
BUT you have to pay shipping (say a fiver minimum for slow transatlantic mail) then VAT on the US purchase price, another GBP3.85. So you're probably looking at a total of GBP23.10 plus at least a fiver for shipping, IF you can find a US retailer who can be bothered.
Unless you've got an "uncle" in the US and you plan on having a birthday every couple of weeks (and can therefore avoid the VAT by claiming each individual import is a birthday present or some such nonsense), it doesn't make a lot of sense to me. And trust me, the USPS "looses" a lot of mail. A LOT of mail. Which is why people use FedEx, UPS, etc. so frequently over here.