So, I tried this today. You can grab singles, doubles, or even four at a time with the support hand out of this and load them easily. Or you can flip the gun upside down and grab Twins or Quads and shove them into the gun that way.
Of course this thing is huge and bulky in this format. But maybe scaled down to a 6-round variant. How to mount it is the next question. I shoved a spare shotcard through the loop and slapped it on the side. Standard 6-shot shell card, as you can see there is even room for another shell (select slug perhaps?). Me thinketh this could be really interesting. But I haven't tried shooting it yet and that could be the Achille's heel of that whole thing.