PX2” STC duo filter bought Feb 2019 from Cyclops Optics, can supply invoice from purchase. Excellent condition. Screws on to any standard 2” fitting. Wade through the dross to find my photos using it here
https://www.astrobin.com/users/ChrisFC/
Currently HK$2,740 (~$500 plus shipping). Asking $375 posted, insured. Now $325