I setup my DI2 on my PC, but you can do it on your phone now with this and the new battery. I noticed battery life has gone down a lot so I am now only planning to use this if I have any adjustments to do on the ride. Nice thing is if you have issues with the DI2 on a ride, you can access the system with your phone to make adjustments if needed, or get out of limp home mode. But, its not an essential piece of gear for DI2, in my view, so 4 stars.
Cant do synchro shift without this battery, and its worth the upgrade just to get synchro shift. I'm not a lazy shifter but it is convenient in a race to not have to think about the gearingcross chaining as you meet hills. Just shift!