I have bought them only with one purpose, to get smoother video when moving and making videos of moving machines in the field. It can be used only for that, I tought that it would help me to get that extreme bright parts in the video back to color but it does not, they are still sometimes white and post cannot fix it.
I use them always but with simple method, I use only Variable ND, put camera in Manual, 1080p30fps at 1/60 shutter, point the camera to the horizont with half sky-half ground in the screen, move ND filter until EV is 0, put the camera on Auto and fly away, DONE. I just want to avoid shutter over like 1/200 and also high ISO and I get that with this system. Manual mode is a no go for me, I dont have the will, patience or the need for messing with the wheel while flying and making videos.
Conclusion from me as an complete newbie and amateur, ND filter videos really do look better than videos without the filter, especially when I make videos of the machines moving and all around is grass, wheat or whatever.