Judging by the underwhelming response, I assume that no one here has ever seen one or is adhering to Mom's advise, "If you've got nothing nice to say...."
Well, I threw one in with my last order and I can now say that I would not recommend one for carrying if you had speed of reload in mind.
The shells must be stacked in such a manner that they are staggered, east/west, so-to-speak and it would a drag to pop a round out of the carrier and into the SG under stress, only to find that you put it in backwards. You might as well carry the shells loose in a bag.
It is probably fine for attaching to the inside of a duck-blind or something such as that though.
Mike