The wrist and hand motion required to shift gears with conventional Time Trial shifters is not only wasted time, but a compromise in bicycle control as well. Shimano uses a two-button interface on the Ultegra Di2 Remote TT Shifter Set that requires minimal movement from your thumb for instant cadence adjustment without a change in hand position.
That's an undeniable advantage to electronic shifting. The fact that your sleek TT bike won't have mantis-like forelegs should also call your attention to these lightweight gear selectors. Another advantage is there are no cables. No cables means no friction.
Also, the system makes fast shifts up or down the range, front and rear. Each shift is the same. Every time -- you'll appreciate the consistency. Better still, you can kiss cable maintenance goodbye. Never again will your shifting performance degrade over time or will you have to fumble with cable tension.
The double buttons have a pronounced surface area to make shifts a thoughtless, fully-intentional affair. The buttons have 2mm of travel, and are as easy to use as a mouse click. Each click of the button results in one shift. If you're coasting, you can pre-shift any number of gears, and the system will engage when you start pedaling.
The Ultegra Di2 Remote TT Shifter Set is not backwards compatible with the Dura-Ace 7970 Di2 derailleurs or wire kits. It is compatible with Dura Ace 9070 11-speed and Ultegra Di2 10-speed E-tube electronics systems. It plugs into the second port of the Ultegra Di2 levers, and can also be used with Ultegra Di2 in a TT/Tri setup without Ultegra Di2 levers by using the SM-JC41 Junction Box.