Wide open the 28mm f4 PC is uniform to the corners,
though not outstanding (by f5.6 it is, and may be shifted a
few millimeters). By f8, in H orientation, it is sharp to the
corners with almost full rise (f11 sharply covers the upper
corners in H with full 11mm rise). For V orientation, f8
gives a few mm rise, and f22 is required for almost-sharp
upper corners with full rise (Nikon recommends 8 mm max in
V, but the lens illuminates fully shifted [assuming a Nikkor
filter and no shade {I don't recommend using a shade with
this lens}], and sharpness is OK at f16 at the top, especially
if sky/clouds occupy the corners [though building details are
OK, I would use f22 with textures in the upper corners with
full shift]). A combination of V and H shifts provides the
least allowable shift, but you can still use most of the rather
generous 11 mm at small stops. AI PC's will fit the TC's, though
operation with them is quirky. Since the mm shift is magnified,
extreme shifts are possible (and the vignette occurs on the
opposite side from the expected), but shift is limited by
sharpness loss from decentering the optical system - so f5.6-8
are about the smallest useable stops [but on the 35mm PC, I
found using a deep yellow filter sharpened the decentered optics
somewhat, making using the 2X practical with extreme shifts in
B & W {the equivalent of almost 22mm of shift, which places the
horizon well outside the image area!}]).

Actually, non-AI PC lenses generally mount just fine - mine is non-AI,
and it causes no problem since the rear is narrower than lenses with
aperture rings (they just won't mount on TC's, due to their different
AI tab arrangements...). The aperture is easy to operate, and I almost
never forget to operate it... You select the aperture (inbetween stops
are OK, if you are gentle with operating the preset wings), and stop
down to that aperture by moving one of two wings until it stops (can
do it at eyelevel with the focus hand...). To meter, you need to center
the lens and stop it down to taking aperture (with the F3, you can meter
with it shifted, short of full shift in V orientation, but in other
cameras, the shifting bright spot in the GG/Fresnel messes up the meter
reading so it must be centered for metering). When I use it, I focus,
then meter stopped down, then open it up, shift it, touch up focus, then
stop
down and shoot - it is MUCH easier than it sounds, and you can skip some
of the steps after the first photo (or for speed shooting, just scale focus
with the lens stopped down, meter it [making aperture adjustments without
the preset mechanism {locked at f22}], shift, and shoot). A grid screen
is VERY useful - people tend to tilt the camera down as they shift up,
giving reverse tilt to parallel lines...;-) You will wonder how you did
without it, if you do much architecture. It is useless for people, unless
you like rearranging proportions of people's body parts.;-) It is good for
landscape, due to the even sharpness to the corners, and the ability to
look up without flattening the mountain (you can even make it a bit
taller...;-) And then there are those droll reverse-tilt photos, shooting
buildings with bigger tops than bottoms, etc...!;-) Or you can use it as a
surprisingly large, but surprisingly sharp and slow, regular ol' 28mm, with
a quaint preset diaphragm...!;-) Or you can simulate medium-format film by
shooting two opposite-shifted frames, and joining the images
(totally useless!).