To some extent I wonder if the additional imaging capabilities of the latest phones (or of a real camera), or post-processing of image series could to some extent bring up with 12 nm filters some of the extra features (eg better contrast) previously visible only with the narrower filters, but without the downside of bandpass shift. In the interesting comparative pics of the linked thread many of the structures highlighted by the 5nm filter are present also in the 12 nm pics, just not as visible.
Longer exposures with a 12nm might bring out similar details. I think the Samsung and some others have the ability to expose longer than iPhones.
the reverse is true for narrower though - less exposure time, lower iso, and some post-processing to clean up noise and scintillation could be done as well with the narrower filters I imagine. Super sensitive regular cameras like the A7S would be fine with the wider notch filters.
I still say for visual, it is a matter of subjective preference. Some would rather see a cleaner visual, more stars, and less nebulosity than see the higher scintillation and rolloff at the edges with a very fast optic. The telescope and focal ratio play a big part in this also. The NV Device too. Variable gain devices have the option to smooth out scintillation by turning down gain. This works with very narrow filters too. I do this with my pvs-4’s. My fixed gain devices, I just put up with the scintillation or try and get a faster, brighter image to smooth out noise by faster focal ratios. If you have a telescope with extremely flat field and can get edges to display without aberrations, you might want to see more uniform views and not go for super narrow notches that might rolloff the signal at the edge also.
All very subjective which is why you see mixed reviews of different filters on the forum. Consensus is an Ha filter is essential for bringing out nebulae detail. Which flavor is the very subjective part. No free lunch for either end of the decision on wider or narrower. For me, a 5nm will be bought in the near future as a compromise between 3 and 7nm effects. I can’t see myself buying a 9 or 10nm, but someone might want or prefer a compromise between 7 and 12nm effects. Harder to find the Ha between 7 and 12nm but they are out there. I think both jdbastro and cnoct have filters between 7 and 12nm.