From the product description Polyfilters remove the following:
Ammonia
Nitrite
Nitrate
Copper
Phosphates
Antibiotics
Dyes
Proteins
Toxic Metals
Insecticides
Ammonia shouldn't be a problem in a correctly cycled aquarium. If you use a filter media that reduces ammonia it will end up depriving the beneficial bacteria and will cause reliance on the filter media. Change the media at the wrong time and you can get ammonia spikes.
Nitrite shouldn't be an issue in a correctly cycled tank as it's converted to nitrates by the beneficial bacteria processing the ammonia.
Nitrates can be a problem if left to build up. The exact safe limits can be confusing due to different sites having different info. Personally I aim for below 20 ppm. Higher levels will lead to eventual organ failure in your fish. I've seen it described where a low level like 5 ppm is like a tee-total person while high nitrates 40+ ppm is like an alcoholic for the fish organs. Some sites put the alcoholic level as high as around 100 ppm so it doesn't seem like a well studied area. Anyway, high levels can lead to liver failure, blindness, stunted growth, and a lower immune system opening the door for other diseases. This will affect young fish more than adult ones. Like alcohol in people some fish will have a higher tolerance than others. Knowing this I aim for as low nitrate level as possible, Taking a fish from a store and adding it to a tank with a much higher ppm can cause death within days to sensitive fish. Generally this will already be managed through regular cleaning of waste in the aquarium and water changes. Some live plants will use nitrates but won't use up high levels. If you have large nitrates in your tap water you can treat it before the water change using a filter material specifically for nitrate removal. Algae can form in ppm above around 10 ppm.
Phosphates are handled pretty much in the same way as nitrates and are caused by the same things in an aquarium. Often overlooked and can cause old tank syndrome. Regular cleaning and water changes fix this too. Interestingly keeping low phosphate levels help prevent the growth of most algae altogether.
Proteins are basically left over food, fauna waste, or dead plant material. Proteins are what break down to make ammonia. Again this is usually kept low by regular cleaning and water changes.
Copper, Antibiotics, Dyes, Toxic Metals, and Insecticides have no business being in your main tank to start with IMO (and those benefits are probably aimed at marine users mostly). If you need to dose your fish a quarantine tank is a better place to do it. However, I do appreciate it's not always possible to keep a quarantine tank in which case this filter material will have a use then.
In summary most of the benefits this filter material offers are not really needed in a well maintained aquarium. Given that the advertising also says it removes 'excess nutrients' it would seem that it would be particularly bad for a planted aquarium.