At a minimum you should be writing your first iteration of a product in something that's clear and easy to understand, if only so that the effort of translating it to something else when needed is less painful. Rails is a great candidate for that.

But even with that being said, prototypes and v1s have a nasty habit of continuing along far past their originally intended expiration date, and if your only criteria is what gets sales today with no regard for future maintainability, you're taking on a very significant debt that is going to be hard to repay when you do need your tech to be easy to work with and performant.