Some members have done them.
Their performance is a challenge to quantify, as their performance is close to testing resolution that we amateurs can perform.
One curious situation occurred in relation to them.
When Hyundai went to the Bonneville Salt Flats to attempt a speed record, they 'abandoned' the air curtains on the race car, opting for MOON wheel covers.
https://www.motortrend.com/news/hyun...at-bonneville/