I guess my take is completely opposite on the REI bivy.
I can get my BA pad inside, never had my bag get wet.
The screen is not the greatest and you will have rain come through if you are out in the open, giving a refreshing little spray occasionally.
I spent 4 days in rain and snow and humidity high enough to make a Kifaru tipi liner rain like a sprinkler with no moisture in my bivy or on my bag.
2 years ago I spent 5 nights out in continuos rain with no issues.