Warnie you are looking at payback periods wrong.
It'd only be 56 days if there were no intermediate payments. But there is a payment every fortnight. If no one makes any payments earlier than required then the theoretical average payback period (not including transactions with first payment on the spot) is (14 + 28 + 42 + 56)/4 = 35.
@mal85 missed something here too - in the US, absolutely every transaction for first time and repeat customers must have first payment up-front. I believe this may be to reduce risk & increase return, and possibly offer lower rates to merchants in the US. The average payback for these loans is (0 + 14 +28 + 42)/4 = 21. This implies a 17x annual capital velocity. Very profitable.
Note even in Australia, all in-store purchases must have first payment up front, all first-time customers must have first payment up front, and for some larger transactions online e.g. > $1000 for repeat customers - must have first payment up front.
Very profitable.
