The lifetime access option shouldn’t exist for an app like that, not unless they have another primary form of income (usually ads). That type of service costs a lot of money to host and if you have a user base that does a one off purchase you stop having a good chunk of that income relatively fast

That’s just the main red flag I see from that, I would be super hesient starting on a platform that isn’t self sustaining and doesn’t have a parent company willing to chuck money at it “till it works” like Google did