I'm not trying to start controversy, but...
I can see how ND graduated filter on DSLR might help with a bright sky, but I don't think they have graduated filters for little tiny MM drone cams? (I might be wrong, those could be handy)
Are you flying in some extremely bright sun conditions and need to bring shutter speed down and lowering EV by -3 is not an option?
People talk about drone polarizers, but how will they use them? They can't turn the ring, or there is some servo mechanical ring turning? (serious question, I know how polarizers work)
I have a feeling all the filter talk is just money grab at the store, most if not all can be done fairly easily in post.
I'm a photographer, I have a few DSLRs full set of Canon L lenses. At the very beginning, I had almost every filter you can imagine, then after a while, I have completely stopped using them, there was just no need beside few rare situations like flowing water effect during the day with very strong ND but you need solid tripod and ball head for that, those still look much better when it is dark and under natural light, when shadows are much softer or nonexistent.
Besides blur effects, no matter how much you spend on the filter it will always vary slightly decrease the quality of the very good sharp lens (I have done many brick wall tests with best quality UV filters). I might occasionally use UV as a protector in a bad environment. Filters might help on DSLR if you do not plan to do anything in the post, in very specific situations. But on the drone, I just can't think of the situation.
Take ND64 that filter will just butcher quality of the photo, but it might still be acceptable in a smaller resolution, it will add 6 stops to your exposure. If you want to create a nice water effect MM will not be able to be steady enough to make foreground sharp, maybe for some small resolution like Instagram, but still, MM moves a lot...
Can someone post an example photo where a drone filter would make a difference (don't post pics from filter ads just your photo)? With Lightroom\photoshop and ability to process 100s of photos with few clicks is it worth playing with filters?