Before you think about touching Ulysses 3, check out MultiMarkDown Composer.
MMD Composer is written by the guy who made MultiMarkDown, its files can be saved outside of the program even when using MultiMarkDown, it only costs $12, and MMD Composer supports Critic Markup - editing annotating for MarkDown files.
Ulysses 3 looks good until you actually use it. It doesn't store plain text files (it stores everything by default in a proprietary DB system you can't access outside of Ulysses) unless you use the External Sources, and if you do use External Sources then you can't use MultiMarkDown or even Ulysses's proprietary MarkDown XL - only plain MarkDown with no image or footnote link-ins. Ulysses also apparently has problems with iCloud Drive, as does it's iPad counterpart, Daedalus.
I'll admit, I'm a bit biassed. I believe a plain text editing program that costs $56 shouldn't be misrepresented as to its capabilities, and what it's supposed to do should work - or be updated promptly when users bring up bugs.
Oh and as to The Soulmen's claims about their high iTunes rating. I've seen mine and several other users 3 star or less comments have been deleted. Take that as you will.