When purchasing my Tarmac I road the Di2 and found it to be pretty darn cool. Road it a bit over 30 miles on a "hilly" for around here stretch. It was nice not having to worry about trimming the FD and all that, and the shifting was spot on. I did end up going with mech though, as it just didn't feel "natural" to me not to move the levers and "feel" the shifting. Ultegra shifts so nice a crisp now that it was about a wash. I'm sure I would get use to Di2 feel in no time at all, but I'm more retro then that