Add a toggle to open/close appfinder
Now that the option to remove the title bar (window decorations) was added, I am suggesting that you also add a toggle to open/close the window via the same key-binding. We have added such a thing to our TROMjaro distribution via xdotool:
xdotool search --onlyvisible --class xfce4-appfinder windowkill || setsid -f xfce4-appfinder
And is very useful. It acts like most such utilities that let you search through your apps. At times is easy for you to press a key, say Super key, and have that popup window (appfinder) that lets you quickly search for a app. But at times you may do that and may want to "revert" back and close the window. Pressing the same key seems like a sane way to do it. Else you'd have to press Esc.
So I strongly suggest a toggle solution for ease of use.