“Markdown notes app” is really like a class of notes apps unto itself. Some people find this surprising, but I personally don’t want to use a Markdown notes app. It’s trivial to create malformed Markdown syntax; it shouldn’t be possible to have a malformed note in Apple Notes. I craft posts for Daring Fireball; I dash off notes in Apple Notes. Frankly, perhaps the biggest problem with Apple Notes is that its export functionality is rather crude — PDF and, of all formats, Pages.