If it's just regular filing, that's something like $70, and the IRS pays the refund in about a week. TurboTax claims they vouche for the validity of the filing, so there's little risk of it not coming through, and even if it does, they can just say, "oops, we can't file for you until you do XYZ" and boom, they didn't finish providing the service.
So, that's a $40 loan on $70 of principle, or 57% for that week. Annualized -- to make it commensurate with other interest rates -- that's (1.57)^52 = a f---ing lot.
R_n = (1 + R_0)(1 + R_1)...(1 + R_n) - 1
It's easier to just use log return:
r_n = r_0 + r_1 ... r_n
r = log (1 + R)
Anyhow, compounded returns aren't the best way to think about this. It's not like they could extend the period and realize the compounded returns.
Payday loans are a similar situation, it seems exploitative to many/most people. But those people who think it's exploitative are the ones who don't need the service in the first place. If you can avoid it, you should never ever get a payday loan. But if it's between a payday loan and missing a rent payment and living on the street, it's a pretty attractive and rational proposition.
Would it be better that a certain segment of the population not have any access to credit? Or is it better that they have access to expensive credit? Moreover, if they want some (expensive) credit, it's pretty paternal and condescending (and sometimes racist) to say that they aren't rational enough actors to deserve it.
In fairness, I may have missed something more obvious in the UX.
You didn't. It's phrased on purpose to not make it sound like you're paying for this "service". And the lettering does not stand out (compare to say all their annoying ads to make you upgrade).