Ok - so this is second-hand feedback here.
A friend of mine, who I signed up with Starling late last year, has just come back from a holiday Bulgaria and said he had no issues at all using his card over there. His first words when I saw him was ‘Starling was amazing in Bulgaria!’.
He loved getting instant updates on his account even when abroad and the only ‘issue’ he had was convincing the shop that he was using the card in to charge it in the local currency instead of in Sterling.
He took £100 worth of Lev (the Bulgarian currency) to cover tips etc, and still came back with £20 worth of it at the end of his trip.
His girlfriend was so impressed, it looks like she’s going to sign up for an account now as well as they’re going to Prague later in the year.