But if you have a few hundred products then this doesn't become so easy. And where exactly does Zapier deliver that file from in a secure way?

If I'm going to go through all that trouble, I might as well just use a Wordpress electronic delivery solution or Woocommerce, in which case, what's the point of this website-less payment solution?

If I'm gonna go website-less, then it needs to do what the website would otherwise do.