I’ve been at it over a decade now and still found the only reliable way to make money from offline App Store apps is good old fashioned paid apps, $2.99 being a nice sweet-spot.

If you had customers buying last year, it’s likely you’ll have even more customers buying next year. If you stop maintaining your app, that stream of new sales almost immediately dries up.

Offline mobile apps which charge a subscription are a very silly fad to me. The few that get away with it are being steadily edged out by someone else who wants to eat their lunch.

I love the OP’s idea and absolutely see the use case. I also think it’s very promptable. My unsolicited advice is to strike while the iron’s hot at $0.99, because I’d be very skeptical if they’ll attract enough subscribers before getting starved out by copycats.