As there is only a handful of lemmy users compared to reddit, I think simply relying on one time purchase is not sustainable for the dev. After the bot accounts purge, there seems to be 1 million lemmy users right now, and only a fraction that is an active users, say, 20% of it (very generous), which translate to 200,000 users. If even 1% of those users bought Sync for Lemmy for $10 (no idea what the actual price will be), it would means 2000 people buy the app. With app store's 30% cut, that means the dev only got $14,000, which is peanuts assuming he'll need to support the app as long as the reddit version (10 years or more?).