Comment by tim--
5 years ago
No, not at all. There are ways to implement this without making it a requirement to use the app. For example, you implement a counter for each user of the app, so they can only use a subset of the API requests allowed for your application.
Then if they go over their allocated amount of calls, or they have been a user for X days/weeks/months, you give them a guided walkthrough on how to register their own API key.
I imagine for something like 90%+ of users, a popup that says "Your maximum number of API calls has been reached, click this link and register your own API key to continue using..." is an instant nope