I can vouch for the DGM NPB (narrow band pass) as well. I have very limited experience but I was amazed how well it worked from light polluted skies. It does not add colour to anything, it just dims everything except the light coming from gaseous nebulae. Well worth the $AU80 I paid for the 1.25". Ordered it from DGM optics, got it in under 10 days.
http://users.erols.com/dgmoptics/