Originally Posted by ColorChange

Well, I"m one of not too many in the world who have gone from RED to Di2 on my SLC-SL. I've had it on for a few weeks and here is my early review.

The performance of the Di2 is devastating. You simply tap and get a gear, fast, any time, under any conditions. That means full load, front or rear derailleur - or at the same time, cross chained or not, 700 watts or more, or less ... do you get the point? Touch and it's done. That's it. You can't screw it up, even when trying. The closest thing I have had to a mis-shift is taking 1/3 crank to catch the next set of pins and ramps to make the jump on the fd. Operator error still occurs every now and then as I am still getting used to tapping the buttons and am trying to perfect my "left side big ring, right side up two gears" upshift or "left side small ring, right side down two gears" downshift. I do these changes at the same time, one tap left side, two taps right side. Super cool! Since shifting is so easy and reliable, I shift constantly, tweaking my ideal desired cadence.

RD shifting is quieter than RED (almost silent unless the FD auto-trims or your pumping major wattage).

I am now running the RED powerdome 11-26 cassette with good results so far. Shimano claimed 11-25 was the largest rear cog that was compatible. It was so cool to throw the new cassette on the bike, start riding it, hit the trim adjustment button, and within 1 minute of putting on a new cassette, I was dialed in and riding. No tools, no twisting cable stops in the bike stand. Too cool!

It does weigh more but this difference can be reduced by using RED components in some areas. I have heard the RED crank will work as well but haven't tried it.

Is it "worth" the extra money? Not anymore than RED is worth the extra money compared to Force. I'm a techy guy and LOVE it. Seriously, it's that much fun. Other people may not care so much.