I think the first was difficult to connect as they were doing it blind from the front whereas when he plugs the Jimi in he is leaning around to look into the back of the IMAC.
It clips on to the vent so presumably the arc in the "J" with the USB port at one end and the clip on the vent at the other helps with the effects of the lever.
Still looks unnecessary to me when a simple extension would do the same job.
My concern is actually that he always grabs the front of the MAC before plugging a cable in which suggests there is an amount of force required. Using a small extension would remove any potential for the MAC to move or for anything to break under the forces involved.