We used our Visa Debit card from our bank this year on Mariner and had no problem. We too got paid half way through the cruise-what happens is that you charge everything to your Sea Pass, and at then end of the cruise, your debit card is charged, just like a credit card would. Nothing comes our of your Debit Card until there is a total for the entire cruise, and then you get a list on the last night of all charges to your Sea Pass Account so you know extactly how much will be taken from your bank. You may also use the television in your cabin to keep track of your Sea Pass Account. I believe that only On-Board things are charged to your Sea Pass, unless you use the Sea Pass Card to purchase port excursions or trips.
Hope this helps-have a great trip!!