I don't find a light curve for the Nebustar but they claim it equivalent or maybe "better" than the Lumicon UHC. That light curve is on the net. Note it only passes the H beta and OIII lines blocking the rest of the spectrum. Objects not emitting mostly in this part of the spectrum will be greatly dimmed by such a filter. CCD cameras while having a peak response, some in the blue green some in the red have a response curve far flatter than the human eye which peaks in the blue green. Thus for visual use such a filter greatly enhances many emission nebula by reducing sky glow and star light but passing the main light emitted by the nebula that our eye is sensitive to. Since we see these in black and white the color is usually lost though some really bright emission nebula do look rather blue green in the filter, M42 and M17 for instance. For black and white photography it would work for such objects but since they emit far stronger in H alpha (but our eye's see this very poorly making such a filter nearly worthless visually) a H alpha filter is normally far better for such objects. Eyes want the UHC, cameras H alpha.

Here's the Lumicon version's response curve. I'd expect it very similar to the Nebustar's response curve. Note the curves stop before H alpha is reached. I believe the Lumicon version passes some H alpha but Nebustar's doesn't based on the Nebustar claim of it being "Red cut-off". In our club members with very old Lumicon UHC filters report no H alpha response but those with more modern ones do report H alpha response but it varies greatly depending on when they were made. Still for CCD work the pure H alpha would give the highest contrast for such objects and is preferable.
http://www.lumicon.com/images/lumico...hart-revsd.jpg

Rick