I used to edit the Zim markup directly in a very basic text editor, so Markor is a big improvement. It offers syntax highlighting, some menu items for things like formatting, and a preview mode. So not wysiwyg, but still pretty nice. It also allows you to easily create new notes from scratch, which is kindof a pain if you're just using a generic text editor.

I do have some issues making nested check box lists (maybe I need to review the Zim syntax) and it's not clear if you can add images. Mostly I review and update my todo items, read notes, and write small notes. For that I've been pretty happy with it.

And syncthing is great.