Great 
I guess, it was my bad too, since I should have checked the structure of my archive and tell you to drop the Zip from the Dmg and not the “outer” Zip. Sorry.
I think I enclosed the Dmg in a Zip because the forum doesn’t accept Dmg uploads (at least back then when I uploaded it).
PS:
I noticed that the only hint that you have to mount the Dmg first, is a tiny line in my 2.1-update post that can easily be missed.
So, for other users, here in bold:
Download version 2.1 of the plugin, unzip it, mount the Dmg and follow the instructions there.