First of all I am a bike lover and a tech guy. I've got the old 105 - have been use it for 6 years now. Last year's spring got the new Ultegra di2 R8100, the same one that is exactly in performance as dura ace - only heavier with some grams. I was shocked how small the performance difference is between old mechanical 105 and the newest electric Ultegra. From the internet comments I was expecting to be blown away, to see a hole new level etc. Bulls**t. It's almost the same, if you are paying really much attention to details, it's slightly faster. That's it. BUT, does it worth some hardcore cash to blink 20% faster? Because those are the differences. From 0.5 sec to 0.3 sec. If You aren't focused You will miss it. Maybe in a crit race some will see the benefits. In every day life it has 0 value.

O, not to forget - 12 speed cassette, pain in the ass as the cog's got closer and closer and the error calibration it tends to 0. If you search, the bike forums are full with people complaining with the noise of some faulty cassettes (mainly 11-34) - mine too.