Not a company to rest on their laurels, Shimano tweaked their new 11-speed 6870 STI dual control shifters with a slimmer, more anatomic friendly profile closer to flagship Dura-Ace version. The shift buttons can be more easily reached when riding in the hoods and button feel has been improved. All the buttons are in the same location as the standard STI levers so the learning curve is virtually nonexistent. The buttons require a light touch and only 2mm of movement for perfect shifts every time. Di2 shifters are as soft as perhaps a mouse click and can be a huge benefit for anyone with hand issues like arthritis or carpal tunnel.
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. They have a reach adjustment to fit all hand sizes. The Di2 6870 STI levers are, in fact, about 115 grams lighter than the 6800 levers. The levers are more sleek with a lower profile and have improved ergonomics designed to enhance long-distance comfort. Shifting can be done while coasting with the derailleur executing the shifts when pedaling resumes.
The Ultegra Di2 STI levers are one part of the Di2 system including shifters, derailleurs, battery, battery charger, and etube cables/wires.