[girvo]

> Why the hell isn’t there a simple “download now, pay if you keep more than 4 hours” kind of option, for example

So, one thing I've seen a _lot_ of new apps do is basically this; but sadly, includes some annoyances itself.

Instead of "download, pay after x hours", they instead have a subscription model gating most of the features of the app. They give you 1 (week|month) free, as that's easy to do with in-app payments automatically. Of course, now you have to remember to cancel this subscription if it turns out it's not what you're after, which is annoying, albeit pretty simple on iOS.