I looked into this the last time I saw Zilch mentioned, as the Afterpay one used by Amazon does work like that. Apparently Zilch only takes a cut from the merchant and doesn't have fuck-fuck fees. If you miss a payment they'll lock you out of the service but that seems to be it. This scares the shit out of me in the sense of building a general consumer debt over what should be the most basic thing a person can afford, but this specific service isn't doing the more parasitic and vicious version of the model.