[BetterRed]

Here's a different idea - but I don't know whether it's doable within the Google/Apple/Amazon walled garden 'ecosystems'.

Give CC away for free. At twelve monthly intervals have a look at the number of books stored on device, and invite user to make a contribution based on book count - e.g. $2 for up to 1,000, $5 for 1001-5000 and $8 for 5,000+. Sure, there'll be those that will decline the invitation.

Having license checks carries the implication that people are dishonourable, whereas an annual volume based voluntary contribution implies the opposite. Most people like to think of themselves as honourable.

Also provides an ongoing revenue stream from happy customers.

This isn't an original idea - its based on something that a couple of my tray gadgets do - they count things and suggest a modest contribution based on annual usage. I always contribute the suggested amount. I never considered buying the Pro versions, even though in one case my voluntary contributions over several years have exceeded the cost of Pro, thrice over!

BR