Editing on Medium
I like it!
Most commands that I need are accessible by selecting and right (control) clicking to pop up a menu. And the help area at the bottom is, well, helpful. If only I hadn’t closed it! Now I’m not sure how to reopen it. Ah — that was easy — find ‘Hints and keyboard shortcuts’ in the menu revealed by clicking the ellipsis button (top right, just left of the bell).
There’s really nice support for images. The Quick images support is particularly good. Help is to hand off the ellipsis menu again.
Mathematics on medium
See ‘How to write mathematics on Medium’ for the full details of what is possible if you are willing to suffer a little. My advice would be to link your Medium article through to a site that has MathJAX or KaTeX installed.