I'm willing to bet that magazine is a 54r Vepr Magazine.
Could be, but Tapco does make mags, so they might have their own design.
Problem is it's an entirely different receiver than the MN, and Tapco doesn't give much in the way of specifics on the system.
I'm inclined to believe that the magazine is mated to the stock
somehow, and not the receiver- and feed the rounds up into the receiver. It's the only way to get it to work (possibly) without machining mods to the receiver.
All other bottom-metal mods, like CDI's, mount to the receiver. Can't do that with the Mosin.
Call me a skeptic on reliability. I'll believe it when I see it work flawlessly; but my bet is it will be many months (like the Mini chassis at the Shot Show a couple of years ago) before it actually hits the shelves.