The Lumicon Swan Band filter works very well, but is clearly limited in it's use to comets only.
Some of the "Light Pollution" filters may also help a little for visual observation of comets. I have a Sirius Optics contrast enhancement filter, which helps a little on comets. I wouldn't be buying a "Light Pollution" filter for use specifically on comets, but if you have one to hand it may help a little and save you buying a swan band filter. If you have to buy a filter and like observing comets, the Lumicon Swan Band is exactly what you need.
I havent used one lol! but i know the swan is popular amognst the pro's, especially when used to view gas comets/tails from the LP city/'burbs - i prefer the 'dark sky location, with elevation' filter for comets nothing beats that!