Unigue has always been a tight fit for me in an AA28cf hull. When I used Unique, the blue PC gave me the best fit.
I never tried Red Dusters with Unique, but use them with Universal in the AA28cf. As you noted, Dusters does say the new Red Duster will work in the AA28cf hulls. Alliant emailed me there is no pressure problems using the new red Duster in that hull with Unique. They said there may be "fit" problems. I've tried a few with Universal and had no "fit" problem. Dunno about Unique.
I heard stories of cold weather problems with the Blue PC, but I never had that problem. But I don't shoot much 28 gauge in the cold.