Counter like this is not kind of app you'd usually expect to bring a lot of money. It's not based on subscription of any kind and doesn't offer any back-end services. So the most logical way of monetization for this app is actually selling it. But there might be more.
Free Multi Counter app allows to use up to four counters at once. When user deletes counter, its deleted forever.
Paid version allows unlimited counters, extended icon set — and archiving option, so counters are stored at cloud servers until user removes them permanently.