Thank you for your feedback, noted in the To-Do list, to develop a native app for every device. About subscription, I'm not so sure as it helps developers to keep working and improving the project, for example, if we opt for a lifetime purchase, users who purchase this kind of offer would be needed to keep using the app to recover the value they paid.
We plan to use iCloud Drive from start, and we plan to add more possibilities to sync data in the upcoming versions.
