I bought this filter to replace a very old 1.25" O-III. The difference in contrast and transmission is astonishing. There were parts of the Veil I had never seen before. North America Nebula's Gulf of Mexico region was extremely obvious, whereas before it was only a faint hint that there was something there. The Helix Nebula went from nearly invisible to jumping out of the eyepiece, and M42 showed more nebulosity than I've ever seen before. The whole loop was striking.
I can't compare this filter to any other premium filters, but this knocks the socks off my old Meade OIII. The differences were not subtle, at all.