There's nothing wrong with writing an app to scratch your itch. But this app could be a web app, and I don't see any value in it being a subscription. The cost of hosting something like this is so minuscule that I'd make it free and just eat the cost if I were running it.
I'm not gonna use a web app with any frequency, especially when I'm already in the car deciding where to go and thus have to use my phone. Web apps are notoriously terrible on phones compared to computers.
I would benefit from the app myself, primarily. And I would need to pay to host it anyway. Others may also make use of it, with no warranty, and no guarantee of me keeping the service running for any length of time.
So you are selling an app whose server could be plugged at any time and render the app unusable. How is that any better than a subscription. Imagine paying money for a phone that stops working after one day. By design. You would be furious. And rightfully so
