Anyone opting for Shimano Ultegra Di2 doesn't have to worry about the technology. You'll be able to exert your fullest effort in even the most extreme of conditions. Ultegra Di2 has been built upon the experience of countless professional cyclists.
If it works for them, then it will work for you.
Levers have been ergonomically designed for maximum control and total comfort. Derailleurs shift as quickly as you fingers can move. One click and the right gear is engaged instantaneously. Di2 is faster than regular shifting systems. In a sprint, a fraction of a second's difference in shifting speed can be the difference between winning and losing.