Well, it didn't make things worse, but didn't make a perceptible difference in noise, either. Plus it's quite hot on the head, with greatly reduced airflow despite the few, token vents on it. All that and it didn't increase my overall efficiency (18 Wh/mi, with recent pre-aero helmet trips between 15-20 Wh/mi), which isn't surprising given my upright riding position, big frontal area from shoulders and torso squared to the wind, and wide panniers without a tailbox.Ear covers may help, not sure how much of a gap there is between the covers and your ears, it could make things worse. A cheaper and potentially more successful solution is just to wear a stretchy type headband that covers your ear-hole.
Therefore it'll be going back to REI for a refund, and I can close out this embarrassing mini-phase of my life.