This is a bit OT (when talking about the slats): Personally I believe if the slats had posed a big problem without providing sufficient advantage they would have eliminated it from later models.

To my understanding some unexperienced pilots were afraid of going to points were slats would open. The reason I imagine is linked to what was said by a previous poster: It was very likely not smooth. So an unexperienced pilot might have been surprised by the rather sudden change in lift and may have reacted wrongly. Someone with experience would have learned to do the right moves at the moment the slats opened.

Another issue was perhaps that for symmetric opening one would have to avoid side slip and there also experience comes in, an experienced pilot likely being more automatic in maintaining symmetric flight than an unexperienced one.

I think I have read some pilot tales that said that the real manoeuvering for them started when the slats opened as the plane then could provide enough lift for tighter turning.