I agree with the sentiment, but everything about the service, apart from the app is metered as well (i.e. keeping the server)

Selling an app is fine, but never sell the promise of something (a service) forever.

If the service is continuous make sure there's a recurrent charge. This is not about nickel-and-diming, this is about keeping your service profitable (or at least covering its costs)

How I killed all goodwill by trying to milk customers.

Which is more-or-less exactly the same as saying "freemium", 99% of the time.