In Australia, they are typically interest free. You just repay it in four instalment payments. I believe they make money through charging late fees and selling purchase history to data miners. I guess that could arguably be cheaper than a traditional credit card that would charge interest for carrying a balance for the same duration of time you're spreading out the BNPL payments. Paying outright would be best, but I guess if you know for certain you'll have the money for each repayment then you might be able to play the BNPL game to make your money go further in order to buy more in a shorter period of time.