The bit that was banned on the Williams was the connection at the bottom of the mirror, which you can see on that picture, was broad and twisted. Mercedes therefore keeps that part straight, and unaltered from before. Sure, it likely still is purely aero, but not as obvious now.
Nice view of the route, between the tub and the barge boards, that air is channeled through to the leading edge of the floor. The air comes from under the tub/above the t-tray and is "protected" and turned by the barge boards ahead of the floor. The air flowing though that channel has presumably been conditioned by the nose cape etc. to some degree.