Hi Tim. The app is not subscription based. It's just like any other purchased application. For instance, as long as your devices are all Android, and you are using the same google account on each device, you will be able to download the app to each device and only have to purchase a single time. The same goes for Apple devices. As long as they are all using the same iTunes account you can download the app to each device on that account. When you purchase an app it is tied to the account you purchase it under. As long as you always use the same account you will always be able to download the app since you already purchased it. One thing you cannot do, however, is purchase on Android and use the app on an iPhone, or visa versa. The app must be purchased at least once from iTunes and once from Google Play since these services do not communicate with each other.