I can believe there is a market for this service, but that doesn't say much for the average consumer's savviness
Debit card numbers, designed to take money out of your account, are what fraudsters want and have compliance policies so strict even bank employees usually don't get access to the full string. Account details are less useful to fraudsters and generally printed all over communications from banks, including the checks and remittance advice handed to third parties.
So why would rational people prefer the latter, particularly if it involves paying a premium?
Is it another startup whose usefulness stems in a large part from the lack of ubiquitous free, same-day interbank payments between checking accounts in the US (unlike much of the rest of the developed world)?