Reliable and proven Di2 technology makes it way to Ultegra for incredibly easy and very precise shifting. The best thing about Ultegra Di2 is you get Dura-Ace Di2 performance at about half the price.
Most derailleurs use a spring and cable tension to move the chain from cog to cog. The Shimano Ultegra RD-6770 Di2 front derailleur employs highly innovative digital technology where an electronic signal is sent to a worm drive motor move the chain from chainring to chainring. Shifts are lightning-quick with no hesitation. Performance is on par with Dura-Ace Di2 except the Ultegra uses a slightly bulkier motor.The front shifting might just be where the largest benefit of Di2 is realized for a couple reasons. Di2 front shifting is proportionately much faster than cable front shifts and this is thought to translate to a few bike lengths on the competition when cresting a hill. Also, front shifts on a cable system can be tough for riders with hand issues like arthritis or carpal tunnel. Di2 make the shifting effort just like clicking a mouse. One of the slickest features of Di2 is the auto-trim of the front derailleur. The front derailleur automatically centers itself when rear shifts are made making front derailleur cage rub a thing of the past.
The Ultegra Di2 front derailleur is one part of the Di2 system including shifters, derailleurs, battery, battery charger, and several cables/wires. The Ultegra Di2 front derailleur is not compatible with Dura-Ace Di2 shifters or first generation cables.