Yes I bought one when they came out last spring.
I would use them in moderation to be honest, it seems to have become default advice to use NDs to improve image quality.
Since the camera is basically an action cam and doesn't have an aperture adjustment this is reasonable.
However they will be almost no help at all for stills because you'd get slower shutter which is not good even with the P3s astonishing stability.
For video the idea is slower shutter gives a smoother recording; you may notice less of that stuttery effect on panning (but painfully slow is still required).
The improvements are rather subtle and you are going to get a slight colour cast which might not be that easy to take out depending on what software you use.
I find an ND4 is often enough in what we in the UK consider 'bright' conditions. I have that and an ND8 but only found use for that so far in bright sun on snow.
If the kit includes a polariser I suspect it will hardly get used.
When taking ground based stills the whole idea is set it up dependant on the angle sun is hitting the camera, and getting it wrong can be pretty horrid.
So the use airborne would be limited though you might still get good effects from it with a well defined subject and shots planned in advance.
Your video will be most improved by shooting LOG with flat settings (try all on -1) then colour grading afterwards, perhaps using simple LUTS as a short cut.
GoPro studio is a good option for editing, and includes quite suitable LUTS which are intended for their own LOG mode which is rather similar.
