It sounds like they're an American version of Monzo. Monzo started out by issuing Mastercard credit cards with a cool app but have since been granted a proper banking license and are now a proper bank. Monzo also wrote their own software.
In other words, Brex may not be a bank yet but don't wrote them off as smoke and mirrors either.
In other words, Brex may not be a bank yet but don't wrote them off as smoke and mirrors either.