EF-D is no brighter, no more precision in focusing manually, it merely adds the grid lines in the viewfinder. Supremely helpful in performing architectural photography with the 40D, as I just did this past weekend, requiring much less need for perspective correction in post processing! Example here...
(For portraiture, the grid lines actually are pretty good for indicating the 8x10 frame area, too!)
The CFn is to adjust the meter only...no AF adjustment is needed at all, since the AF sensor never knows what screen is in place...it is at the bottom of the camera and gets light from the secondary mirror behind the main reflex mirror.