Mark, two things on the Omega OIII + Hb: you're missing the point here on this filter - with any filter there is give and take. While in the strictest sense it may be not as you say a "true" OIII, the band pass of Hb is an added bonus. Second, have you tried one? If you haven't, what do you think you will see through it?
It is disconcerting when people are all to quick to dismiss something without trying one. Break the chains, people. If money is a concern for someone looking for a filter, this OIII + Hb filter (which is what it is labelled as) I think is a fantastic solution. I have looked through "true" OIII filters, and this filter does very well - the tiniest bit brighter. BUT, if an additional UHC filter is too expensive, or just too many filters, and you want to see something like the Horsehead, this OIII + Hb filter will show it, and just as clearly as a dedicated UHC filter. As a practical and economical filter compromise, this one is excellent.
This is why Omega offers this filter under its "Omega" brand, not their "DGM" brand where you will find a strictly "true" OIII filter. But what they haven't done, unlike some other more popular brands, is mislabel their filters as one company labels their "UHC" and it really is a broad band LPR.
Scepticism is mandatory. Experience is Nirvana. With the amount of eyepieces you've gone through Mark (and you've had one or two,
), you certainly would know this. This OIII + Hb is a different take on astronomical filters. Bloody good one I reckon.