This Consumerist post describes a problem with this verification process when you initially fund a new Ally Bank account. It's not a problem if you're careful and correctly enter your external bank account number. In the case described in this Consumerist post the person entered her checking account number rather than her savings account number. She assumed that Ally Bank would first require verification of the trial deposits before the debit of the account. However, the debit occurred before the trial deposit verification. This caused the checking account to be overdrawn triggering NSF fees. She described the process she had to go through to get these fees refunded.
There was also the concern about how this process could cause a debit of another person's account. However, another Consumerist reader provided her experience with using the wrong account number in the verification process. She was funding the Ally account with a Bank of America checking account. Here's her description of what happened:
Bank of America then denied the transaction because the account information didn't match up. An Ally CSR called me to let me know and I fixed my account information over the phone. The second time it went through without a hitch. I had no fees, by the way.
One thing that I've found useful when I open liquid accounts is to initially fund the account with a small deposit. In addition to avoiding problems as described above, it can avoid losing access to a lot of money if it takes a long time to finish the account opening process.
Another issue to consider with the trial deposit method is that some banks will also debit the two trial deposits. So if you create the link to an external savings account, the link will cause 3 withdrawals which may put you over the limit of 6 which is the maximum number of electronic withdrawals allowed under Regulation D. This could result in a fee. Ally Bank does not debit their trial deposits so this isn't a concern.
I have more discussion on the issues and restrictions with ACH transfers in this post on PenFed ACH transfer policies.
For more information on Ally Bank and the savings accounts and CDs, please refer to this post.
Thanks to the reader who mentioned this Consumerist post in the bank deals hub page.