That's a new one on me.  Seems to be a concrete example of the old adage, "Just because you can do something doesn't mean you should do it."    

Hunting with my Dad's old single barrel, break action gun was always a pleasure because that gun carried so well in the field.  It was a 16 gauge Harrington and Richardson and if you thought you might need a quick follow up shot, or two, the drill was to grasp the ends of a couple of shells and hold them between the fingers of the support hand.  It seemed workable to me at the time and didn't affect the handling/shooting characteristics of the gun like the device in the video would.   A double gun of modest origins likely wouldn't set you back more dollars than a single gun and the cost of the Alofs device would and it would handle better in the bargain - or so it seems to me.   

Interesting video though.  Thanks for sharing.