As I often advise startups, there is never a rule; especially with consumer facing and modern technologies. However, to get you in the right direction regarding monetization, I usually tell my audience a good differentiator between subscription and inapp (unlock) should be frequency and type of use.
If you have a static knowledge base you're giving, subscription is best.
Non-consumable in-apps should only be used if you can structure your startup to deliver new ones regularly.
Consumable in-apps should be for something that gets executed, a function, therefore not good for content but perhaps some kind of medical analysis?

Also, don't forget subscriptions are much more lucrative now but don't be tricked into picking what makes the most money without keeping in mind what is best for your offering.

Obviously more than glad to further discuss if you can give me specific answers in order to find a winning strategy.