I tried using this recently. I had 300 mining ships I organized into fleets via 'Defend' orders on the leader. Then I chose the 'Random Mine' behavior for their leader and made sure to check the update subordinates box.

At first it seemed to work, but after a few hours the mining ships began spamming me with 'cannot sell' messages, along with a loud negative beeping noise, which I couldn't determine how to stop. Even turning off the global settings for alerts for every category didn't stop the spam.

I had to cancel all the behaviors to prevent the spam.