First, the new fabric weight seems a bit lighter and more flexible contributing to ease of use on the Garment Pannier. Additionally, packing the cover into its carry pocket feels faster than the original, which I appreciate after a rainy commute (Seattle, WA.) Second, because of the lighter fabric, the stowed rain cover lays flatter, which I like because it means less of my bike and gear projects into the road lane. Third, the brightness of color seems greater than before or maybe this just seems so because I used mine so much? :-) Fourth, the cover keeps my Garment Pannier and contents mostly dry.
Now for some cons. It seems that the new cover does not fully-envelop the volume that the original cover did and I have noticed that when the cover is installed; only the corners of the cover are able to wrap around the Pannier bottom edges. Memory insists that the original draw-cord contained enough elastic to allow a complete wrap of the bottom edges. Last, when the cover is installed, there’s a tunnel about three inches deep that my taillight sits within. 2WG’s Priority Rear Bike rack might solve this issue by a bracket that extends the position of the taillight.

Pros:
Lighter fabric weight contributes to ease of use
Brighter color for increased visibility
Dry! Garment Pannier is protected from rainfall

Cons:
Perceived reduced volume coverage—parts of Pannier exposed at lower edges
Tail light sits in tunnel formed by Pannier and rain cover (future solution is planned)