Question #1: What would this mag accomplish? MP44's already have unreliable feeding as is because of the mag well angle, having another chunk of lead and steel dangling from the mag catch will certainly not improve the situation.
I don't believe there's ever been a dual barrel MP44, as the seller claims. And if one even existed, with a mag configuration like this, the two barrels would have been too close together to allow the left side to eject without interfering with the right side. Unless they moved the left side ejection port to eject out to the left. I call bullshit.
I can build a mag setup like this in one hour, give it the classic Polish seller "just found in the attic" treatment (wrap in vinegar soaked rag for a day, then leave it outside for a week), come back in a week from now and present another "rare" mag. What color do you prefer, blued with rust spots or mottled phosphate? The latter takes a couple days more because I first need to remove the blueing before phosphate and vinegar treatment. It will come with a COA and capture papers.