You’re probably aware of this already but the other difference between the UCM and D’Brake is how they mount. The UCM floats on both bearing cap bolts while the D’Brake is tightened hard against the rear bolt ear. You can see how the D’Brake is offset to allow for this in the pictures in this thread.
I’m not sure whether it makes a difference in practice, but the UCM might be slightly less forgiving of poor setup when it comes to vibration.