> I will need to be selling 200 copies every month as long as the app exist only to get basic level of income
First of all, it's probably an unrealistic expectation that a small utility like this should be able to provide you with a basic level of income.
Second, in terms of pricing, you seem to be trying to make moral arguments about greed and scams here. But you should simply be realistic about the demand curve, and try to maximize your profit. If there are a lot more people who would buy this as a one-time purchase than as a subscription, you'll be losing money going the subscription route.
I'm not really interested in maximizing my profit, I simply don't want a burden. If people like it, use it then they pay for it and I take care of the app and if not the project dies off without me having to support potentially thousands of customers for years to come.
First of all, it's probably an unrealistic expectation that a small utility like this should be able to provide you with a basic level of income.
Second, in terms of pricing, you seem to be trying to make moral arguments about greed and scams here. But you should simply be realistic about the demand curve, and try to maximize your profit. If there are a lot more people who would buy this as a one-time purchase than as a subscription, you'll be losing money going the subscription route.