Q: How much does this piece actually reduce drag?

In simulation, when paired with the Carbon Efficiency Spoiler, the system reduced drag by approximately 40 newtons, about 2.4 percent, and improved net downforce by about 534 newtons using a transient CFD model with 30 million cells. That figure is for the combination, not the extension alone. On its own the extension still adds rear downforce and cleans up the wake; the biggest numbers come when it works with the spoiler.