I have never owned the Contarex Bullseye but I did own the Contaflex Super BC for quite awhile. I absolutely loved those lenses, but loading film in that interchangeable back made loading film in my Leica III seem like a walk in the park. I almost wish I had it back when I look at the images again. Almost, but not enough to go buy another.
I do suspect that if I had used it more I would have gotten more adept at loading it and probably would not have minded as much. Ah well.