Most commonly the slice. So now you have a starting point to correct your problem. Continue to use The Whippy until you can hit is as well or better that you regular equipment. Try to eliminate that flex in the shaft that you feel when pulling from the top. Use your hips and shoulder turns to keep the shaft straight.
Centrifugal force is the key.
The Harder and faster you swing the club head, the more rigid the shaft becomes. Not completing the Back swing The Whippy TempoMaster, with its flexible shaft, forces the golfer to finish the back swing. You just can't hurry the club from the top. In order to hit TWTM well, you need to start into the ball with your turns and not with your arms or hands pulling from the top. Just remember to swing the club back and swing the club down.