I think the objection is not that they're charging a fee, it's that the fee is $39. TurboTax (just the basic federal edition) is what, $30? And yes, this is essentially credit, extended for what, a month? So ($39/$30 * 12) is yearly rate of like 1,560% for that credit, aka., highway robbery — that, I think, is the parent's point.
(I might be a bit off on the price, but not enough to change the result. TurboTax's loss if the debtor here "defaults" somehow is … what, even?)