Dan Coxwrote a review of Shimano Di2 TT Remote Switch SW-9071 on March 1, 2014
Familiarity: I returned this product before using it
These shifters only work in conjunction with the Di2 TT brake levers having the integrated shifters. This is because these shifters have only ONE button on each bar end. I have the HED corsair bars with the integrated brake levers, so once installed these levers would shift my Di2 9070 rear derailleur up and down, but we could not shift the front derailleur whatsoever. Came to learn that what is needed in a case like this is the Ultegra SHI0651 bar end shifters, which have 2 buttons. I am not sure why Shimano assumed we would always want to go to our brake levers to shift our front derailleur, but anyway, these are only meant to be secondary/satellite in function for your TT bike.
p.s. - I bought these as part of an overall bike order and specifically to suit the previously purchased HED cockpit. I had help from customer service in making the right choice, but in fairness the info I gave is pretty clear in the part description up above. These do function properly for moving the rear derailleur, without a doubt, just make sure you know what you need before ordering.