This is not a brand name diagonal and was just a spare prism I had, but I bought a very good diagonal mirror with a 1 3/8" minor axis from Joe Sansuri and mounted it. Images appear as good as my Televue now under very high magnification. I just don't need it anymore because I only have 1 non-newtonian left.
I think $30 + shipping is fair, but like always, let me know if you think it is worth less. Fred