Interesting that you should bring this up, Stephen. I bought the DGM Optics NPB filter (cosmetic second) last time the exchange rate was favourable and I am very happy with it. It does a great job on the Carina Nebula in particular. Lots more things I haven't tried it on as yet. I now want to buy the DGM Optics OIII filter (2").
Anyone interested in joining my order to share the postage cost? Took two weeks to deliver last time I ordered.
ps. DGM Optics say "Star images retain a much more natural color..." Eta Carina turns violet!
The rest are fine.