I really like a clean right-click context menu so it would be good if 'Open with Fly' only showed for the items that can be previewed with the app.
I'm currently seeing it for PDFs, Fonts, PPTX, XLSX and just about all other file types.
It would be nice to also have an option to hide 'Open with Fly' entirely if I decide to set the app as my default double click behaviour.