This weekend I tried the plate holders for my Rolleiflex with Harman Direct Positive paper in lieu of film. I cut down 4x5 in paper into two 6.5x9 cm sheets after removing a narrow margin.
The day was overcast and very dull, so I used ISO 0.75 (two stops below ISO 3). I got clean whites, but very little shadow detail, owing to the inherent contrast of the paper. I had to open up to f/4 to handhold.
Still, the results are pictorially interesting, and could warrant more experimentation. I think macro would look especially good, since enlargement is not possible, and would give me a reason to make good use of the ground glass back and Rolleinars.