No matter what you pay for an ND or any other filter, any piece of glass (or plastic) that you choose to put in front of your camera lens will degrade your image. You may or may not be aware of the loss of quality in your image but it will be there. Anything that you put between your composition and your lens will always reduce the light and detail reaching your sensor. Similarly, there are hundreds of thousands of photographers out there wearing an ND filter worth cents on a lens worth thousands, that will never realise the full potential of their high priced glass because of this. And it's usually because they've been told "the filter will protect you lens"! That's a job your lens hood will take care of guys!
But back to your onboard camera. I live and work on one of the sunniest continents on Earth, (Australia) and have never needed to use ND filters on a drone camera for my work. My tip to get the best imagery from any camera you own, learn some basics and understand how aperture, shutter speed and iso come together to produce a correct av (exposure value), then produce the purest imagery you can without filters or software hacks, ( "creative" camera settings etc ), then adjust in post. Works for me!