I don't think Di2 shifts a lot better than a good mechanical group. Maybe a little. The auto trim is wonderful and works better than manual. There's no maintenance required ever, except charging the battery which takes half a minute on my part. It's easier to use with thick gloves. You can add buttons. Your Garmin can term you what gear you're in and count shifts over a ride. It's overall better.

Shifting more than one cog is faster and more natural with mech. You can't misplace your charger.