They aren't the worst ways to monetize, they are just the ones that work.
> How about this? Just charge one time fee for major versions of the app. Minor and patch versions are free. Keep the privacy oriented aspect and local to users machine.
Unless he is charging a substantial and/or recurring amount, there is no way he will put up with angry customers and enjoy maintaining the software in the long term.
Plus, if this is hosted, hosting is a variable cost that always goes up, so his prices for updates will always be increasing.
