ACH and direct debit win on cost, but the conversion picture is more nuanced — asking a consumer to hand over bank account details, rather than tapping a familiar card, introduces a trust step a card checkout doesn't require.
Push vs. pull, and why it matters for conversion
A push payment — where the consumer initiates the transfer themselves without handing details to the merchant — converts more comfortably than a pull payment, which requires collecting banking information directly. That distinction affects checkout trust more than most merchants account for upfront.
Where it actually earns its place
This tends to convert best for larger transactions, where the cost savings over card processing are meaningful enough to justify the extra step, and for recurring billing relationships where the consumer only has to clear that trust hurdle once.