Even with a double I was always prepared to reload as quickly as possible in days of yore. The need wasn't there for shooting at the next flight to arrive, but I had to do so several times with cripples on the water and no dog. I just needed to get off a followup shot quickly before the bird recovered enough to move out of range or into deeper water. Sooooo, I ALWAYS tried rapid reloads just for the practice.
In my case back in the days of lead, there really weren't any specialized products around, so I had to improvise with plastic film canisters and technique. One of the quickest methods I found when using plastic wads was to mount the wad over the nozzle of my shot snake, which then served for a seater. I seated the wad into the muzzle, filled it, then rammed the loaded wad home rather than seating the wad, then pouring. Truth be known, I usually placed the overshot wad before ramming the works home. It was suprisingly fast to do it that way- just pour the powder, assemble the payload at the muzzle, and ram it home with one stroke.
The devise you describe sounds like a way to accomplish much the same thing without the shot snake getting mixed into the fray, if I understand it correctly. I'm sure inclined to try it.