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Hi Gordy,
The filter you have is not a narrow-band Hydrogen Alpha filter, but a wideband or more correctly low pass filter which starts just before the Hydrogen Alpha wavelength with 50% transmission at ~640nm and ~90% transmission at the Hydrogen Alpha wavelength and near 100% transmission at the SII wavelength and beyond. It would certainly be useful for limiting light pollution, but its wideband characteristic may take in too much into the deep red/infrared to the extent you may see some star bloating, if the optic you are using is not extremely well corrected. See graph below...
Best
JA
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