It seems simple enough and the concept seems logical, but I do not think this type of drill will help a golfer stop flipping thru impact.
As I've posted here, I still believe in categorizing golfers as either 'hitters' or 'swingers' even though I believe that technically golfers will do a little of each in a swing. But for the sake of making it a bit more clear to understand, labeling a golfer as a 'hitter' or a 'swinger' by what they predominantly do in the golf swing I believe will help them find and execute the swing pattern for them easier.
So with that, here's why I don't like this drill.
Hitters push with the right arm/right hand. Swingers pull with the left arm/left hand. So for the 'hitter' (and remember, I truly believe that the majority of golfers are better suited to be a hitter), this drill really does not apply.
For instance, the pic of my latest impact position where I have a FLW after impact
The FLW (flat left wrist) was executed by concentrating on my RIGHT HAND, which would keep my RIGHT WRIST BENT. In this case, it was the 'drive loading my #1 Pressure Point into the base joint of my left thumb.' Again, you can read up about it in my 'Hitting Revelations #2' post at (http://3jack.blogspot.com/2009/05/hitting-revelations-part-ii.html)
I've done the 'swinging' pattern for a bit as well, but didn't have nearly the success with it as I do the 'hitter' pattern. However, what I do know about the 'swinging' pattern is that it is very pivot driven. So a big part of having a FLW at impact in a 'swinging' pattern is to have the pivot move effectively enough to where the hands feel pretty passive throughout the downswing. Or you can simply pull the club downward, like you're pulling the rope to ring a large bell and then try to 'bang' down the #2 Power Accumulator at the ball. I really cannot imagine any very good golfer who does not flip who does it by consciously feeling that they are keep the flat left wrist at impact. Perhaps I'm wrong, but I really doubt it.
It's one of those things when you actively try to focus on the left wrist being flat, you inevitably flip. But when you focus on other parts and you execute it properly, you then start to feel a noticeable difference.