Tony,
Just saw this today. You may be interested as it’s clip-in filters for the D750 :-
https://youtu.be/7wd1hRM7I1o
It seems that maybe the Optolong clip-in’s may not vignette as much as the STC DuoNarrowband did for my D810A. However the video does discuss about other caveats with these clip-in filters (especially with wide angle lenses).