I've played with Shopify for many years and it just can't do some of the low-level stuff I want it to do without badly mangling how product taxonomy works. Coins are a different kind of beast than typical retail and if I'm going to be writing code anyway, I'd rather write my own code (vs. writing code "on the shopify platform").

The really sensitive stuff - financial stuff - they handle through checkout (and I don't need anything special there), so I've really just written my own catalog & front-end.