I'm sure these will be perfect for someone, but I am curious about your own use, since you apparently weren't using any filter when your aircraft drowned. Did you find that to be the case?
The owner of the filter set for sale with the bird that drowned posted in #308 above. He's only made 2 posts. I use my set all the time with the GR4 by itself and also accompanied with either the ND8 or 16 usually to blue out the sky more and it does a good job. I haven't had a reason to use the ND32 even though I tried it once and it is nice. The great thing about this set is that the filters are glass and can be stacked together to enhance any type of day and it works nicely even on totally overcast days making post enhancement not needed. I don't take stills with this camera, I have a Sony A6000 that works great for stills and movies on the ground. The clean color of these GR filters are what make this set a cut above the others.