Six years of running a period tracker app with no subscription, no ads

I've been running Simpluna, a period-tracking app, for six years.It's a company based in Tokyo, Japan, but development and operations are basically a one-person effort.The app is built with React Native (Expo).The defining trait of the app is that it's simple, with no unnecessary features.Recording periods, calculating predictions, and sending notifications — that's the core of it.This space is dominated by big players (Flo, Clue, and in Japan, Luna Luna).Building something similar would have been hopeless, so I made the things those apps don't have my selling point.Optional features beyond the basics are offered as one-time purchases.

Most apps in this space use subscriptions, but I didn't want to.Subscriptions make revenue easier, but they're a mechanism that keeps manufacturing reasons not to cancel, and features keep piling up as a result.By staying away from subscriptions, I could keep the app simple — a tool that doesn't intrude on the user's life.With privacy in mind, data is stored locally on the device by default rather than in the cloud.So far, the app has found a solid footing in East Asia — Japan, Korea, Taiwan, and China.It has almost no name recognition in the West or elsewhere, but there is a small number of users in those regions who like it and keep using it.

The reality, though: the app is profitable and covers its running costs, but it's not yet at a level that supports a living, so I have no choice but to keep it going alongside other work.I see this as one of the costs of not taking the subscription route.I have two questions.How do you see the difficulty of sustaining an app on one-time purchases alone?I'd love to hear from people who made the same choice, or who gave up and moved to subscriptions.The other: could an app like this be accepted in North America and Europe?