Good deal, Magic...I never got the wing nut thingy...whatsatfor?
Until you have that Slip Cover option in your hand, it is difficult to envision how it works. The cover has more holes in than Swiss Cheese and is intended to adapt to about anything you can put on it. There are 4 holes to attach your Garmin Cradle in the same way that you would to the Smaller Chrome or Black plate. The cover is made from a hard machineable Plastic Material. This slips over the larger Chrome plate. From under the chrome plate you pass the "wing screw" through the hole and into the plastic (threaded hole) on the slip cover.
It is a nice set up but as I mentioned, unless you have a quick disconnect on your power cord, you would need to remove the GPS from the Garmin Cradle to disconnect your cord. The Wing Screw is not the most secure but anyone with allen wrenches can can remove the complete unit in a few seconds.
While on this subject, in one of the earlier pictures it shows a plastic cover over the GPS when not in use. Is this model specific or an after market option? I have the 2610 and it did not come with that cover.