As a fellow developer, I don't mind paying for a good work. But this app should be a one time payment, not a subscription ;) Subscription today is overused - in my opinion, it's only understandable for services where the actual content is a product and is always changing on a daily basis - such as netflix, or spotify or newspapers.

Not for regular apps, which are only updated few times in a year and month-to-month changes are usually minor or none at all.

For example, you've updated your app last time 7 months ago - so by what right should users pay you every single month? :) I understand it's convenient to get money for nothing, but it's just shady monetization strategy for majority of the apps.