I had some free time today so I was curious about how aero my "aero basket" really is. I did some coastdown tests (here it is on Strava https://www.strava.com/activities/593351260 but I used my own data capture device). I had to throw out more than half due to passing cars corrupting the data but I wound up with two clean runs for both with and without the basket, which had little variation. I'd have liked to do more but I was getting tired

Conditions 0-2 mph wind gusty from the North and NorthWest, which is why I had to throw out one anomalous fast downhill from both sets. 90° F, 40% humidity 29.9 pressure. I started exactly on the same crack in the pavement each time and rolled, no push-off, and kept the same line of 8-12 inches right of the right tire track. By coasting down without pedally, only the force of gravity propels me, so the speeds reflect drag and rolling resistance.

Here are the speeds with and without the aero basket:



Surprisingly the aero bag tested out faster than the bare bike, so perhaps it has a faring effect after all. I'm a little skeptical due to only two samples of each configuration so I'm going to call it at least a draw, with a good possibility that the aero basket is faster.