@D_Rehak, many thanks for the motivating feedback!
W.r.t. to business models, I’m personally no fan of subscription-only models. And for me (as a former polar researcher with elongated field trips, see here) I strongly favor apps that can also work fully offline.
Ideally, the app would be free for individuals and money would come via other means (think Zotero). But as this is highly unlikely, I’d like to pursue the classic one-off license model (i.e., no subscriptions for individual users). But before I can think too hard about things like this, I want to focus on the app, make it stable and bring it into release state. As you say, there’s still much hard work ahead.