Does this have any advantage over the system-provided combination of control-command-D (which works with or without a selection).
One thing I don't like about the pop-up is that it appears for whatever word your mouse is hovering over. This command can work with a selection or caret placement. Which means for keyboard junkies, they can skip one more trip to the mouse.
The only other advantage is that you might prefer using the app to the pop-up.