Just another take on the above really. The way to manage a Bronica in my view is to wind on completely immediately after an exposure. Indeed things get kind of black through the finder or prism unless you do so, and it isn't really tenable to re-apply MLU before winding on, not least because you can't see to compose. You use the collar round the shutter button to prevent accidental exposure.
Wound -on, the S setting on MLU raises the mirror and the finder blacks out. The shutter will fire in this mode if the camera is working properly, but it will be much quieter than when not using MLU. Of course it requires that the basic conditions for firing are in place . After exposure the screen remains blacked out until you wind on fully.
In C setting the act of winding on will bring down the mirror momentarily during the winding process, but by the time the wind-on is complete the mirror has reverted to up and you can't see through the finder. As indicated C is not really appropriate for single shots.