Neutral Density 4 with Polarizer (ND4/PL): This is the most commonly used of the two ND filters. It is a 2-stop neutral density (ND) filter which is used for filming on mild days, i.e. partly cloudy or during the golden hours. This filter helps reduce highlights as well as reduces lens flare when shooting into the sun. Adding the exceptional quality of a Polarizer this is a workhorse filter.
Neutral Density 8 with Polarizer (ND8/PL): This 3-stop ND should be used on mildly sunny days. This filter helps prevent lens flare, and reduces any most rolling shutter. This filter also slows the shutter speed enough to blur the propellers when they are in frame.
Neutral Density 16 with Polarizer (ND16/PL): The GO-TO filter on sunny days, this 4-stop ND will dominate your collection. The polarizing aspect of this filter reduces glare and increases colour saturation.
The following guideline is a good starting point for when to use each filter while filming with your Phantom 4, Inspire 1 or Solo. The goal of this chart is to reduce the cameras shutter speed to 1/60th to give aerial videos a smooth cinematic look, rather than a choppy high shutter speed look. A popular way of filming aerial video is to have your shutter speed at double your frame rate. So, if you are shooting 1080/60, then you want to try to achieve a 1/120th shutter speed. Or, if filming 4K/30 or 24, you will want to be near 1/60th shutter speed.