It's an improvement to the gun altogether.
Up until I tested both drum and plug together, I looked for other people's results but the board was quiet. So I'm posting my own experience. I guess no news is good news.
I shot the gun before with drum/AGP mags using cheap low-brass (Winchester, Federal, and Remington bulk packs from Wal-Mart) and had consistent jams -- FTF/FTE roughly at a rate of 1 in 5. Slugs and buckshot seemed OK though, but I didn't try a lot of that.
Last weekend I tried again with the new gas plug and I have to say that those problems are fixed -- no jams! Ev