Bingo, mod parent up. CurrentC is a DO NOT WANT for lots of reasons (especially access to medical data), but making it an ACH payment is a TERRIBLE IDEA.
You have the legal right to tell your bank not to pay out debit transactions that cost more money than you have (overdraft). If you decline overdraft "protection" (really, "can you please rape me with fees" protection), the transaction will fail and you will be charged neither at the POS nor a fee from the bank.
You sometimes have a similar option with your bank, to not pay out ACH transactions that cost more money than you have. BUT, if an ACH payment presents, and your bank declines (per your instructions), they will charge you a fee equal to the overdraft fee anyway. And the merchant/whoever that submitted the ACH payment could have you for a bounced check fee, too.
As to GGP's sentiments... class, raise your hand if you keep a handwritten checkbook ledger of all your paper, electronic ACH, and debit transactions. Now, keep your hand up if you also cross-reference each of your entries against when the bank actually pends and posts all your transactions. Ok, look around you. The rest of us use technology so we don't have to spend hours doing that. And we ought to be able to trust that technology to say if there's enough money in the account.