I’ve just got back from a few weeks in Nepal using my Starling card. For the most part I was using it to withdraw cash but used it a few times in shops/hotels.
Everything worked fine from Starling’s side, but I had a couple of issues. Firstly, not all ATMs work with Mastercard - this wasn’t really a problem as it just meant trying a few ATMs until we found one that supported Mastercard. Secondly, most ATMs providers charged a fee for making withdrawals which was a pain (this ranged from about £2.50 to £3.50), again this is out of Starlings hands.
No issues when using the card to pay for things in shops.