The new design is stiffer, smoother and functions even better than its predecessor, a significant achievement to say the least. The new form of the external pieces allow the rear derailleur to move at a different angle and the new internal design will pull the chain closer to the cassette. This translates into better power transfer, more secure grip, better chain/cassette interface and a longer life for consumable components. The chain will now grip more teeth and as a result disperse energy across a larger surface area, increasing the life of the cassette and lengthening the lifespan of the chain as well.
By allowing the derailleur to work closer to the cassette in every position the athlete can now take advantage of perfect alignment between cassette and rear derailleur in any given gear.
The new internal structure of the rear derailleur also makes for easier shifting on the higher end of the cassette as it eliminates any resistance that could be encountered when moving the chain onto the 25, 27 or 29 cog. In short, the athlete will enjoy the exact same performance with an 11-29 cassette as he or she would with an 11-23.