Hi Steve,
I have used both OSC and mono cameras and IMO I believe that the time savings is not as great as initially perceived. Since a OSC
has the bayer matrix overlaid on the chip it obviously loses a bit of sensitivity. Therefore to come up with an equivalent image in terms
of resolution, lack of noise and color saturation more time is needed in imaging. OSC cameras love very long exposures to make up for the
lack of sensitivity. As for narrowband imaging, yes it can be done but you have to keep in mind that when doing so only about 25% of the
chip will be used at a time so additional time would be needed to capture the details. I've only done Ha with my OSC but have seen others
that have done OIII and SII.
Lastly, when processing, while it is possible to get good results processing the image in color like a dslr, the best images that I have seen
the processor has always broken down the image into its separate RGB components - so you might as well go for color if it fits your price range.