Bloomberg shines a light in this article on how hard it is to build a challenger bank. UK challenger Atom, which began offering savings accounts in April, has only 1,800 customers, who have deposited £16M ($21 million). Monzo has distributed 35,000 prepaid debit cards on which it says £31.7M have been deposited. Those are indeed tiny numbers in a country with 70M checking accounts. Will the big banks end up copying them or absorbing them?