The first compromise to note is the true light gathering capabilities of the APD. Below is a table of the exact f-stop markings found on the lens, which is quite handsome, for whatever that’s worth.
56mm f/1.2
f/1.2 f/1.4 f/2 f/2.8 f/4 f/5.6
56mm f/1.2 APD
f/1.7 f/1.8 f/2.3 f/3 f/4.2 f/5.6
As you can see the amount of light lost by the APD filter goes down as the lens is stopped down. This makes perfect sense given the appearance of the APD filter, which looks like a circular graduated neutral density filter.
It must be noted that while the light gathering is impacted by the APD filter, all other aspects of the wide aperture like depth of field are not. Depth of field and “bokeh”—the quality in which a lens renders out of focus backgrounds—are different things.