Seems quite good - I've tried a LOT of MarkDown editors over the years, but until quite recently, I'd stuck with Zettlr for a long time. I've recently reinstalled my laptop, which made me look for alternatives to some software, and I've been playing round with MarkText for the last few days, which seems nice.

HelixNotes is definitely good - if I had to drop MarkText, I think I could get on well with it. I like that they have a debian repository, so I can keep it updated with the usual system update software. I downloaded the AppImage as a quick test, but it didn't work because it was compiled against an old version of glibc.

The only thing I don't like so far is the format toolbar is at the bottom of the editor screen, and I haven't found a way to move it.