That looks terrific and the price is fair. I am concerned about no open source local client - I don't want to rely on the company if it goes belly up (which is why I actually like paying).
I just recently moved to Org Mode but if I were still in the Markdown ecosystem I would give this tool serious consideration.
open-sourcing is on our roadmap (https://roadmap.acreom.com), when it comes to the data ownership & privacy, acreom is built on technical decisions to deliver both in full fashion.
it's local-first, all your data is stored on your device as regular markdown (no custom md flavor) and works fully offline.
I'm working on something similar (i.e. a content editor for developers) with Vrite, that's already open-source: https://github.com/vriteio/vrite
It's not the same as acreom (leaning more towards a CMS-like platform with API, real-time collab, etc.), but is well-suited for e.g. creating knowledge bases.
I just recently moved to Org Mode but if I were still in the Markdown ecosystem I would give this tool serious consideration.