The idea isn't to completely abandon cards right away. You could add LeetPay as a 'pay by bank' option to your regular checkout flow. As a business, your end user would then have an additional option.
Essentially, everyone I've spoken with has expressed a desire to save on fees (value prop is clear), but they've also grown accustomed to a particular way of accepting payments, mainly through cards, and it works well for them. The feedback I've gathered suggests that businesses using subscription models might be a better fit for LeetPay, as it's much easier to debit customers on a monthly basis.
I agree, it's a hard sell to use 'pay by bank' for a single payment transaction. Perhaps focusing on subscriptions could be the way forward for it. In this case the saving is much more clear per customer.