I have 6800 mech and I love it. It does not require any trim adjustment at all in any of the cogs really. It never misses a shift and if it does then I need to start looking at the cable and fraying. I have had it happen twice that I road in the small cog due to rear cable break. That said the bike was still rideable and I came home put new cable on before any electronic would have gotten back battery power. I am not at all against Di2 but right now my 6800 is not broke and I won't fix it. It shifts pretty effortlessly even the front. I have 6700 on my other bike and while is shifts fine it does require a bit more effort.
Like many things on this issue I am not in a hurry but eventually I probably will go to disk brakes. Most of my gripe is in press fit BB and I still find exposed cables much easier to deal with so I in the middle of all this for new technology on bikes.