I would say in most situations close to zero. Just look at all the beautiful cinematic landscape videos done with M4P recently!! I believe all without ND filters. I fell for the hype of ND filters and 180 deg rule too. But TBH unless you shoot...
When did you last see a video that demonstrated the negative effects of not having ND filters on a drone for normal video shooting? Yes, in special cases they are needed. We all were taught the 180 degree rule but how much difference does it...
M4P has cluster of electrical contacts behind the existing clear glass filter attachement it currently sells with. That indicates that the drone is at least hardware ready for the eND. So to answer your question, yes it should work.
LOL
Reporting back as promissed:
After experiencing long satellite acquisition time in my home after updating to FlyApp 17 I decided to roll back the FlyApp to v.13.9. on my Rc Pro. Bench tested after the roll back at home on the same spot...