The first telescope I ever had -a Toya made Tasco 50mm refractor - used a prism. I still have the diagonal here too - in all it's 0.965" goodness
I have used and still own mirror diagonals and dielectric ones, and I am not sure they show the same fidelity - when I looked through the Tak first yesterday, my mind was playing tricks on me and I honestly thought I was looking straight through a tube, not initially realising I was looking at a perpendicular image - they are astonishingly clear and show no internal reflections I can see (whereas the dielectric I have scatters some light on the walls of the diagonal etc.)
May get a Baader-Zeiss one of these days, but for now, in my limited visual role, I will stick with the Tak.