As I wrote above I've bought the second DJI filter set too. For my videos I am using ND 8 or ND 16. Besides DJI maybe prefers to sell 6 instead of 3 filters I find both collections make sense to me.
ND 8 is useful in sunlight and instead of having ND 16 available you could increase shutter speed to 1/100 for compensating one stop more light. (I shoot video at 25 fps @ 1/50 sec normally)
Today I went flying to get some experience in using ND 64 and 256. These make a lot of sense when doing hyperlapses. I did some direction locked flights with flying along a row of trees in the foreground.
Take no.1 was with ND8 @1/50 (ISO 100). Result was heavy shuttering of the trees while they move thru the image. The hyperlapse was set to 5 second duration and one shot every 2 seconds, drone speed 2,5 m/s.
Take no.2: ND64 @1/4 sec
Take no. 3: ND 256 @1 sec
Both about 2/3 of a stop overexposure which looked nice and also ISO 100.
No foreground shutter - trees just move very smoothly thru the image. The filters (resulting in longer exposure time) create a nice motion blur for moving objects closer to camera.
Since
MA2 has the option not only for filming but also for doing stills (what I like a lot) I find DJI's choice which filter to put in which set OK. So if you've got the fly more combo you're covered for testing all possibilities of the drone.
OTH: A set of 4 filters (8, 16, 64 and 256) would have been all I needed...
That's at least what I find.