Sorry, a little late here but my biggest challenge for new students to overcome is the "flip". I think there are a lot of reasons why people flip...incorrect concept, making the ball the target, poor face/grip, improper sequencing, etc.... Brian's C.O.F.F. is a great video and I've used some of the drills but I just feel this is what separates the "Rec" Golfer from the "Advanced" Golfer. Certainly it could be said Flipping could be because of Mental or Physical traits.
Flipping is the result of not doing the twistaway.You can do it on the backswing and then hold the twist coming down(Dustin Johnson) or you don't twistaway on the backswing but do it on the downswing(Ben Hogan and harder to do in my opinion).
Flippers may twistaway going back but then "untwist" coming down negating the good work.Or they don't twistaway at all during the backswing or downswing.
I think understanding the correct mechanics of lead wrist rotation goes a long way to fix flipping but I agree it is a big challenge.Trapping the ball and delofting the clubface is not easy to do in a full out swing.