I think I know what they are saying in that text, but I still don't quite get it.
They are asserting that the "twist" increases the power of the backhand without adversely affecting the forehand, thanks to the shaft geometry difference on the two sides.
Unless there is a designated 'front' side and a 'back' side on these racquets (like on the tilted-head and bent-grip racquets), how is this difference achieved?
From their illustrations (in both the righty and lefty iterations), all I can see is that when the racquet is held in a conventional grip, the upper shaft connects to the grip on the palm side (in front), while the lower shaft connects to the grip on the knuckle side (at the back). During a forehand stroke, it's the upper shaft that is closest to the ball where it connects to the grip. During a backhand stroke, it's the lower shaft that faces the ball. Why would this have any differential effect on power generation?
If one shaft has a different flex characteristic as the other shaft, and the racquet behaves differently depending on which shaft is connected to the grip on the palm side (in front) and which is on the knuckle side (behind), then rotating the racquet in one's hand would flip the flex characteristics, regardless of whether one is hitting a forehand or backhand.
Or am I missing something obvious?