I don't understand your assumption that users are buying iPhones only to use this app and not, say, to also make phone calls and browse the web. In the past, p

I don't understand your assumption that users are buying iPhones only to use this app and not, say, to also make phone calls and browse the web. In the past, people bought iPhones even when this app was not available, and they paid more. You should be asking instead if it's economical to invest $2 into an app to save 40 cents on ketchup. (And, if you plan to make more than five such purchases, the answer is "yes".)