I bought a cheap monochrome camera for the Raspberry Pi to use in a spectrometer. Turns out it has an IR cutoff filter, so all light above 660nm is lost. I may yet scrape off the IR filter, but I’ll probably buy a proper spectrometer instead. It is interesting to regard its images: surprising resolution for a 640x480 sensor, and what looks like at least two stops of increased sensitivity.
For normal photography, I get why some would want a continuous monochromatic sensor. Me, I prefer capturing a bayer-encoded image and grayscaling it; there’s a lot of interesting manipulation to be had in messing with the colors before doing the grayscale.