The App Store is awesome for users, and to some extent for developers too, but it's a known issue in the iOS/tvOS/mac developer comunity that the App Store has a sustainability problem. This usually makes it very hard for developers to justify the development of apps past the initial version.
Showbooth Go is a professional tool, we are aware that it won't sell the volume of a consumer app, and because we'd like to keep developing it further, the work we put into it must be justified by its profit and revenue over time. No comercial software is able to survive without being profitable.
That being said, we are treating Showbooth Go as a service, and we've chosen the auto-renewable subscription model of the App Store, and priced it at $19.99 a month.
We think that this will allow the app to generate an acceptable stream of revenue, making it possible for us to keep working on the product, updating it regularely, giving great support, fixing issues fast and adding new features, increasing its value for our customers.
Even though it uses the subscription mode, you can still try it out and build your own slideshows without a subscription, the only limitation is that it won't play the slideshow for more than an hour without a subscription.