Major takeaways:
1.5% write-off rate for their jan 2020 vintage is very healthy - comparable to the long-term trend for unsecured superprime consumer debt. Given the (I suspect) lower average creditworthiness of Affirm customers, this is a great number. I'd be curious to see their long-term trend for same-age vintages, however. In consumer credit it's well known that all the stimulus support in 2020 has significantly depressed defaults. It would be interesting to see if this is a fluke, or if this is actually what their charge-off rate actually looks like in a normal environment/part of a bigger trend.
I'm a little skeptical of their claim to use ML & build a data moat for significantly better underwriting decisions. Consumer credit laws in the US so severely restrict what you can use for credit scoring purposes that better underwriting through data is basically a lost cause, absent some specific customer segment that has special credit situations.
Finally, as others have noted, 30% of revenue just from Peloton is an enormous number.