I have been testing it for the past hour and I really like it.
I've spent a lot of time (waaaaay too much!) in the past trying to decipher NeckFX's unfathomable settings, trying to find meaning in the completely meaningless descriptions of what each adjustment actually does. More through luck than judgment I managed to arrive at settings I was happy with, ones that work in VR, and work to complement the sustained g-forces from the G-Seat/G-Belt combo. The missing part was simulating the natural image stabilisation that our eyes and inner ear do so well in the real world, which this app does as well as Real Head Motion, which is praise indeed.
I've already deleted all of my other NeckFX settings and will be using these ones from now on.