I've used this on a 5D, 1Ds, 1DsMKII and 1DsMKIII with no interference issues at all. The tab on the back has not been as issue. It is possible that there are versions where you might have to file the tab.
I've also had the Nikkor 20mm 2.8 MF, and I literally could not see a difference between the two. The Zeiss 21mm Distagon is better, but it's better than almost anything and has that wonderful moustache distortion.
That shot was in such a small room that it required an 18mm lens. There was almost no place to put C-stands, and from I can remember, I did multiple exposures for different parts of the room - with a light stand or head in the frame for one side and then combined with another frame without the stand. There was also one exposure for the room that had lights reflected in the window and a second with the room lighting down just for the room beyond the window.
This made a beautiful magazine cover and a great 24 x 36 inch print for the Atlantis Recording.