Advantages of a Mamiya RB67 KL lens over the C lens?

[Alan R. Estes]

To me the main advantage is the Bulb release to reduce shake at the end of long exposures. Also am assuming that I could use a mechanical shutter release timer there to more accurately time those.

Others, I have read about, would be-
Better quality control.
Newer.
Better glass coatings.

Does anyone know of any others that might help me justify buying one.

Specifically interested in the 140mm.

Thanx, Alan