products look much like those from KolariVision, including the prices. These outfits are probably getting the glass from the same suppliers -- Schott glass being my best guess as to the source.
I'd also guess that they are selling it "as is", which I found was not appropriate for at least some of the Sony and Zeiss lenses. Note that long lenses, like telescopes, will not have any problems with the glass thickness.
I think I found my way to Kolarivision via some positive reviews on the internet.
My interest in the astro filter (visible light plus extended red for some specific spectral lines in astronomy) was due to my experience with Kodak Technical pan's similar response curve and its outstanding B&W rendition. If I were to carry only one filter in the B&W film days, it would be a deep orange. The astro conversion is a bit like having a very light red filter on the camera, though note that tungsten lighting is warmer when it comes to setting the white point.
I actually am not a fan of infra red B&W at all. The astro filters give a very traditional B&W look, with, as best I can tell, improved red channel dynamic range.
It would be interesting to be able to compare to a Leica monochrome, but for me the ability to do the multi-color filtering in PS is too valuable to go the monochrome route. I am rather confident that the Sony with the astro glass is a better combination for my type of photography.
I will continue to update my PDF at http://www.paulroark.com/BW-Info/KolariVision-Astro-BW.pdf
as I gain more experience with this B&W approach. It is obviously not what I would consider a "mainstream" approach, and I make no recommendations. That said, after testing the astro cover glass on my "old" Sony a7r, finding the flaws in that thin filter, but also seeing the results, I opted to convert my newer a7rii with Kolari Vision's "thicker" glass. Moreover, after testing that, I am not sending it back. So, I obviously concluded that for my type of photography, this investment appears to be a positive move.