To answer your question .. the dongle has nothing specific to do with Follow Me. It is just the wireless receiver for the remote control. You need a dongle for each MD you want to use the remote with ... when these were still being sold, you got one with the remote, and could order any number of additional ones, per your requirements. You just plug them into a USB port on each MD and they are pnp installed and configured - no further action was required.
On the remote, you hit Connect - this causes the remote to go out and determine which dongle has the strongest RF signal and bind to that. The assumption being that this will likely be the MD you are nearest too. The Follow Me button does much the same thing, but also "bookmarks" the media playing in the room you are in, then the second time you press it, in another room, it issues a DCE command that causes the media playing (and environment) for the user the remote is registered to, to be transferred from the old room to the new room. That is the main functional difference between the Gryration and Fiire remotes.