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For galaxies you want a broad band filter. Light pollution filters are still broad band, they just minimize the transmission of light mostly in the sodium range. They often exclude extreme ends of the blue and red ends of the spectrum too. UV/IR.
Take some time to have a look at the visual spectrum and understand the wavelengths and where they reside. Try to develop an understanding of what the filters are aiming to achieve and you’ll be much better places to make these decisions. Narrowband filters by virtue of their narrow band passes make the variety star colours very hard to distinguish. They are intended for use to show a specific wavelength of light from a specific gas. A galaxy really is a compact source of all wavelengths. They are also normally imaged with a surrounding star field ( colour you wouldn’t want to loose ) so a broad band filter is the way to go. Aliens may also have sodium street lamps but it’s unlikely we’d be able to see them so we can cut out that wave length ( light pollution filter ). Yes you can enhance a galaxy image by adding in narrow band data to show pockets of Ha for example but you still want a broadband galaxy to add it too.
If you’ve made it thoigh all my babble and just wants a brand and a model to buy, I’ve recently been working with an Optilong L-pro in Bortle 8 skies and I think it’s the beat broadband filter I’ve used so far.
Cheers
Ryan
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