I am using Starling Bank. As far as I know they are profitable - they offer enterprise services (payment processing, etc) and use that to subsidise free consumer-facing services.

What I don’t understand however is how the other challenger banks didn’t see this coming. Like how do you decide to build a bank and take millions of VC funding without a reasonable path to profitability? Also I think Monzo could’ve done well had they not taken VC money and spent it all - they do have a good product, they could’ve charged a token amount for it (1£/month?) and at scale it would’ve been decent revenue (they’re at 3 million customers now).