I pay a sub for some desktop software I use. I don't have a problem with it. If you estimate that the average user will use the product for N years, you can ch

I pay a sub for some desktop software I use. I don't have a problem with it. If you estimate that the average user will use the product for N years, you can charge a one-time fee of X or a yearly sub of X/N and make the same amount either way (assuming you got N right and forgetting inflation). A yearly sub is very simple to explain. And people who use the product for longer pay more, which seems fair. The sub also helps to finance the ongoing costs of development and support.