I have used it, don;t own one. Yes it's a normal 28mm if you don't use PC. The controls let you fine tune images to correct vertical/horizontal lines but otherwise is a fine lens.
If I remeber correctly there is a little distorsion/vigentting at corners when shifted and fully open.
Schneider make the 28 mm PC-Super-Angulon in Nikon mount - the fully manual mount is easy to change and, in addition to the mounts listed by Schneider, there's also a mount available directly from Leica. B+W make a special filter holder (for unmounted 74 mm filters) and hood for it. It's a very nice lens whether shifted or used as a normal 28 mm lens. I use mine on my R6.2 and on my FTn/FE2.