The only historical account I have read of the Me410's turrets came from the perspective of a Spitfire Mk IX pilot in Italy. He and his wingman encountered an Me410, probably a PR version, which dove to the deck to escape them. The Spitfires pursued but his wingman gave up the chase. He was slowly closing on the 410 so he kept at the tail chase. The 410's tail gunner proceeded to empty his guns at the slowly overtaking Spitfire without ever scoring a hit. The 410 was subsequently shot down by the Spitfire.
As to the slats, I am not aware of any WWII slats that did not deploy independently.