From the developer's point of view, subscription makes more sense as people benefit from continual development and updates, and the dev continually gets paid for their time.

I paid $1 or $2 for sync pro like 9 years ago and back then, it took a lot to get me to pay for apps. The more I use the app, the more I got for my money per hour spent using the all. But the more work the dev did after he got my money, the less he gets paid for his labor, per hour.

Nowadays, $1-2 feels like a steal for an app, especially for a one time payment. I haven't paid for ad-free or ultra yet, but I intend to because he's shown a long history of listening to his user base and updating/fixing things in a timely manner, which that type of service also is something I value as a customer, even if it isn't a tangible benefit.