FuelForThoughtwrote a review of Shimano ST-R785 Di2 Hydraulic STI Lever & Disc Brake Caliper Set on September 6, 2018
Familiarity: I've put it through the wringer
These brakes work. The major downer is the excessive free throw. The tip of the lever travels 3.5 cm. Compare to 18mm from SRAM levers. What this means is that braking 1-finger from the hoods is very difficult. This is a widely reported problem.
The newer Shimano brakes are much better.