ND filters will definitely help in post when it comes time for color correction. But could you clarify what you mean by a "jerky shot"? Is it jerky in that the actions of the camera (ie: tilt, pan, follow) are jerky as opposed to smooth like using a fluid head tripod? Or jerky in that the recorded video seems to jump frames?
The first will require using a lighter touch on the control sticks, and perhaps turning down the gimbal speed in the pilot app. If you're really brave, you could try changing the control response time in the app as well, although I haven't actually seen anyone in the forum who's done that. One tip that seems to work well for dampening down the controls a little is to raise the stick height. There's a video on youtube on how to do it.
The second is where the ND filter will help out. It will allow you to lower the shutter speed so the changes between one frame of recorded video and the next aren't as great. This gives you a more natural and flowing look to your shot. Less hyper real a la Saving Private Ryan.
Here's a link to a good video explaining the principle;
Good luck with the movie. Could lead to great things.
PS: the vid is for the inspire 1, but the app is the same for both I1 and P3, and the principles are the same.
