By good filter I mean one of the 2 premium branded filters from either URPro or Magic filters, these cost a little more then the generic red filter sheets but from what Ive seen give the best UW filter results, They are specifacally designed to filter out the dominant colours in the water and there are also various options for different types of water conditions.
There are plenty of generic "Red" filters but many of these take away too much light or dont filter out the proper shades for best end results, there is a price difference between these brands and the cheap generic ones but what I was trying to say but probably didn't come out as intended. Paying the little extra for the premium UW specialized brands is pretty good value compared to what you pay for video lights. In terms of results you will get much better bang for your buck with a good filter compared to a cheap light setup which will still cost 10x more then these premium filters.
Lights are still a great option and if you are willing to spend the money its great to have both lights and filters to choose from as they both are good in some conditions but not so great in others, but if money isnt growing on your trees and you want good results without emptying your savings account these premium filters will be a pretty good investment.
I have used the URPro filters with my GoPro's for quite a while using the Blurfix by SRP and have got great results with that setup, the results Ive seen from people using the magic filters and backscatter setups are the only other filter that gets comparable results. From what I have seen these dont hold up to deeper depths as the URPro range but in the shallower waters results are pretty good. I havent used them myself yet so I intend to do some comparison tests to see how they work as filters and general designs for ease of use underwater.
I will be doing a filter comparison between URPro, magic and a generic filter by Oculus for the gopro dive housing, Im just waiting on the magic filter to come in from backscatter. I'm mostly interested in comparing the URPro and magic filters at different depth levels and I also got the occulus one to see how a generic one stacks up to these 2. These 3 filter options are the only "good" options you will be able to buy IMHO, the URPro version by SRP is not for sale yet, I was just lucky enough to get an early test version to try out along with a few other testers around the world.
Its possible to get some basic cheap gel filter sheets and find a way to use them, but these most likely wont give as good a result and will be more cumbersome to use then those designed specifically for this housing. The real cheap ones you can get on ebay for a few dollars are worth a shot as your not going to lose much if they dont work well but I wouldn't spend too much money on them. If you intend to use it quite a bit getting a premium filter will give best results and be the easiest to use and the boost I have had with URPro filters on my GoPro's makes me not ever want to dive in daylight without one.