you're right. Upon further research it looks like NTTA works at airports...
I wonder if one costs more than the other initially? I do remember dropping someone off at DFW Airport and freaking out when the toll guy told me I needed to pay because my TxTag wouldn't work there. Luckily, they took debit card.
I see NTTA a lot more frequently than TxTag for what it's worth.
up to three cars you have on one credit card, they deduct 20 dollars, 4 or more they deduct 40 dollars at a time...i think they when the available funds get below 10 dollars, they deduct 20 or 40, depending onhow many cars you have tied to the one acct