Well, I just finished reading Quantized Accelerations by Mike McCulloch. I skipped some of it that is just enumerating scientific anomalies and attempting to explain them, because that's written to convince physicists and I'm not a physicist who needs to be convinced.
I've attached the 3 most relevant pages relating to the reactionless thruster. It seems that there is *a* formula for describing the thrusters, and that formula is fairly good at describing trusters which have been successfully built, but there are still unknowns, because if this formula Just Worked then building "flying car" class thrusters would be something you could do in your kitchen - ergo people would be doing it.
There seems to be a general lack of understanding of the Casimir effect WRT how the plates block the quantum vacuum. Placing a material which reduces speed-of-light between the plates causes the effect to lessen - but the narrative is that less energy between the plates causes energy on the outside to squeeze them together, so slowing light between the plates should *increase* the effect.
What seems to exist is a formula which describes how well the effect will work, WHEN IT WORKS, but changing the setup to maximize the effect can cause it to just not work.