Agreed. Subscriptions make sense if it's a "business" app, i.e. something you are using to run your business, e.g. Adobe CC, Office 365.

But this one looks like personal app, with little in the way of corporate functionality (Kanban boards, todos, etc). Why not charge a flat fee for 1 year of updates, and make updates optional after that?

I have the same beef with the makers of MindNode, a mind-mapping app for MacOS. It's $2.99/mo which is not much, but I chose to go with SimpleMind Pro because it was a flat 25 EUR.

Developers know the term "write once, deploy anywhere". How about "charge once, use forever"?