The Dura-Ace Di2 STI levers deliver precise and comfortable control. Because the levers don't need to house any shifting mechanism due to the Di2 design they can be made as light and ergonomic as possible. the Di2 7970 STI levers are, in fact, about 150 grams lighter than the 7900 levers. The levers are more sleek with a lower profile and have improved ergonomics designed to enhance long-distance comfort.
Shifting is faster with a different action versus the 7900 STI levers. The unidirectional carbon brake lever is fixed so it does not move like the 7900 levers. The paddle closest to the handlebar shifts the rear derailleur into easier gears and onto the large chainring with the front lever. The shifting force required is very light and only requires about a 2mm movement of the paddles. Shifting can be done while coasting with the derailleur executing the shifts when pedaling resumes. The Dura-Ace Di2 STI levers are one part of the Di2 system including shifters, derailleurs, battery, battery charger, and several cables/wires.