Anyone who makes a big deal about how great the optical quality of Bader diagonals are should test them and compare the results with the older German made versions. Yes, they're still really good but not as good as the German versions. Takahashi uses high quality Japanese prisms and I have been reading an increasing number of comments from users who feel the optical quality is better with the Takahashi prisms (mechanical design is better with the Baader though).
The older "German made versions" of the prism diagonals with the high quality military specifications, have been mostly manufactured by Rodenstock in Munich. If manufactured for the astronomy telescopes, they would cost a multiple of what we are paying for even the most expensive Baaders.
I have the 1.25" Takahashi zenith prism diagonal, and the Wild Heerbrugg 60mm zenith prism diagonal, and my preference is towards the Swiss made Wild, no doubt.
The unique advantage, and the marketing proposal by Baader are the thin film technologies on their prisms and mirrors, and that's why I have the Baader BBHS 2" zenith mirror. So far I know, Baader applies the thin film technologies in Germany, the rest is made in Asia-Pacific, but as always, nothing is for sure today.
Moreover, it is the art of anodization, or another metal surface treatment, which allows to make a guess where the parts are coming from.
Even with the microscopy eyepieces made in Germany, I can tell you in a blind test if they are coming from Zeiss Göttingen, or Leica Wetzlar vs Singapore, just feeling the outer surface with my fingers.
Other indicators for the area of origin are some details in the optics, especially the mating of the lenses into the doublets or triplets.