Posted before on this thread with an update. Had my Tarmac di2 comp for about 2 months now and really enjoying it.
I purchased the climbing shifter and the wireless unit for it to connect to my Garmin and nice additions. It is great to see what gear I am in while riding, change screens and battery levels. Full synchro shift is on which has worked well for me. Do like how you barely touch the shifter and it shifts or holding it down.
Overall it has been my first experience with di2 and when/if/ever I get a mtn or gravel bike it will be di2 as well. You can live w/o it but really great to have.
As far as putting on my emonda with mechanical I personally am not but my buddy was going to upgrade his bike to di2 as he justifies the expense is less than buying a new bike.