Agree that the tendency exists but don't see the tradeoff between transactional and messy in this example--you should be able to create a new product with options [...] in the same request, perhaps using /options to ascertain what's available before posting to /products, depending on the situation.
maybe a more illustrative example of where this can be messy is where a customer has placed an order for a bundle of products A B and C, and there's no "order bundle" API that can do that operation atomically, instead the client code trying to place the order has to call a bunch of random stateful create-product APIs to attempt to construct each product in the bundle, and deal with the mess if suddenly some bundle items error while others succeed. bonus points if some of the create-product APIs are not idempotent.
"congratulations, we've provisioned the bundle A, C, C, C that you ordered! sorry about B!"
