Have used both the Starling card and Apple Pay in Hong Kong, worked fine.
In Hong Kong, when you make a card payment on a foreign card, some
vendors give you the choice of whether to choose HKD or GBP. Be careful to choose HKD to get the Starling rate rather than the vendor rate.
Although I was offered a choice of currency, and selected HKD, because of the immediacy of the transaction notification, I was able to see the vendor had chosen GBP and their exchange rate.