It is a purchase of the app and its features or a subscription when it passes 12 months I no longer have those features. I have to pay again
It is a little of both. You pay for a subscription for premium features and those features are yours. After the subscription timeframe, you can choose to renew to subscription for the next 12 months get new features that the app releases. They have done an awesome job and are very quick to respond to feedback. I hopes this help.
I see it as a purchase of the app at a specific point in time, where you get the app’s existing premium features, plus any that come in the next 12 months. If you do not pay again after 12 months, you do not lose any of those premium features.
If this were a subscription, you would lose all premium features after the 12 month period.
I don’t think we could have explained it better, if you’d like to go more in depth, see this blogpost from Drew