ND filters are helpful when shooting video since they allow you to slow down the shutter speed (by reducing the light) to get more natural footage (see this video for more details). If you're getting a lot of reflection off the surface of the water, polarized filters will reduce/eliminate those reflections (even in photos).Should I use a special or polarized filter?
You can find a list of commonly used ND filters here. Check out this thread for a comparison of many of the filters from that list.Should I use a special or polarized filter ?
Do you buy filters from DJI ?