"interest free" deserves quotes. It appears to be so because the installments have the same value but in reality it's priced in the overall length vs price.

The installment culture is so pervasive in Brazil a lot of places don't even bother to show the full price (a vista). And some of them refuse to give a discount if you want to pay the full price now. Not because it doesn't make economic sense, but it's simply not an option a regular employee in major retail stores is even allowed to do, as companies default marketing and systems to installment payments.