Starling have just added a few screenshots of their app to their site.
The Payments options look good to me -
Debit Card options are functional, if a little plain & cluttered (there’s no need to display Lost or Stolen Card until the card’s ‘Inactive’) -
But based on these shots (there could be more functionality elsewhere in the app), while everyone loves a slider, they’re nowhere near as clear as what Monzo are planning, when it comes to displaying interest accrued, fees (they use an interest rate, rather pounds & pence) or what you’ll pay by the end of the month 
