I found the multiple ways of getting into the Dingus a bit confusing at first. You have File>Open in Dingus…, which opens a file, as you would expect from a command on that menu, but also Preview>Open in Dingus to open the current document. The indication that you're not going to present an open dialogue (no ellisis) is pretty subtle. Perhaps this should be rephrased, something like Inspect in Dingus?
More seriously confusing is Help>Markdown Dingus, which I expected to show me the Dingus help, instead of opening the Dingus, where I had to click on the ? to get the actual help.
Feel free to ignore these comments, which are purely subjective. Other people might find these commands entirely intuitive.