I've owned Marked 2 for quite a while. For some unknown reason it's file opening behaviour changed. From it's install I set Marked as the default file for opening Markdown documents. At first it just worked as you expect; double click on a Markdown file and it opens in Marked. Then for absolutely no reason the double click causes TWO instances of the file to open. It seems that others have the same problem going back several years. The developer seems unable to resolve it.
I have changed over to MultiMarkdown Composer and find it Ok, not quite as good as Marked was.
Marked 2 is a nice MultiMarkdown file viewer but it has a really annoying habit of opening every file TWICE! I have reported this several times and it seems this has been an issue for several years. The developer's response is "I can't replicate this problem (so by inference it does not exist)!"
I am using MultiMarkdown Composer and ByWord.
It would be really nice if the macOS version of Textastic could preview Markdown files like the iOS version.
Customer support service by UserEcho