Well, this does cover those who might want to try a H-alpha nebula filter with a white light filter, but does *not* cover those who might try the H-alpha filter "bare bones". This is a danger which I felt needed to be mentioned (not to mention that it wouldn't work either). As I noted, the white light filter with the H-alpha nebula filter would dim the H-alpha detail considerably, but you still might need to mention up-front that the H-alpha nebula filter will not work *period* due to it being too broad and would be risky if it were tried solo. That would cover all the bases.

As for the visual spectrum, when I first made a simple diffraction grating spectroscope in the 1970's, I had a hard time identifying any but a few of the more prominent lines. I quickly picked up the Sodium D-doublet and H-Beta, along with the G-band, but with the bright sun, my eye was immediately drawn to the dark broad features both in the violet (the Calcium lines) and in the deep-red (the Telluric lines of Oxygen). H-alpha took a while to isolate (and only after some effort with a chart of the solar spectrum). It is obvious to me now, but compared with the others, it isn't exactly the darkest or most prominent absorption line in the visible spectrum. Clear skies to you.