What business model should I use?

this product

I have a side-project that I used to offer on the App Store (iOS) for free.
But I failed at maintaining it due to the lack of process and interest just a few weeks after the initial release (3 years ago). Not great at all.

But now I have just upgraded it to be able to work with newer devices and wanted to keep improving it over time, but this time I want to do it in a sustainable way. For that reason I'm would love to get your advice on what business model would make more sense for this type of app.

The app is called RESTer and is a tool to test HTTP requests using your iOS device (E.g. like Postman/Paw but for iOS). Should help mobile and web developers introspect explicit request from the devices to some endpoints.

These are the current models I have in mind:

• Free: Just offer it for free until it is more mature, has more useful features, etc.
• Paid: a simple 1-2$ payment to use the app
• In-app purchase with ads: Place a banner within the app and offer the user a premium alternative that removes the banner and adds some extra features. E.g. backup support
• Another?

The app is here but I'm testing it as a paid application: https://itunes.apple.com/us/app/rester/id1022985409?mt=8

In case you want to check it out without paying please send me your email and I'll invite you as a beta tester (You'll only need an iOS device and TestFlight installed).

Thanks!