Shifting a cost forward a couple months interest free is a great deal for people who are financially responsible, especially if you have some other loan (like a mortgage) that you could be paying off more of instead.
It's no different to the practice of using a credit card for everything and then paying off in full a month later because the credit card interest is lower (often zero if you pay off within a month) than the mortgage interest.
I briefly looked into this, but I wasn't convinced the juice was worth the squeeze. My cash is automatically getting ~4%, but there's too much fine print to make sure the BNPL rate really is 0%, I'm sacrificing 2% cash back, and missing one payment makes the whole endeavor negative ROI.
I suspect this is where some buyers will get into trouble. Theyll think they made a payment, or they miss a notification that tells them to send this month's payment to servicer X not Y, and before they realize, boom they are in default and owe all the interest.
It's no different to the practice of using a credit card for everything and then paying off in full a month later because the credit card interest is lower (often zero if you pay off within a month) than the mortgage interest.