In a dairy-packaging study I used EEG, gaze, and natural observation. One shareable recommendation was simple: add instructions for using the fruit cup.
The distance between those measurements and that recommendation matters. Collecting signals and producing a useful design suggestion require separate checks.
Give each method a job
EEG compared early responses, gaze examined visual paths, and observation recorded picking up, opening, and eating. I discussed the results around common task steps, without treating them as three votes on the same claim.
A fixation alone does not establish preference or understanding. An action may not explain its motive. When evidence conflicts, I revisit context and interpretation before combining results.
Another signal brings more work
Another device brings acquisition, synchronization, cleaning, and interpretation. Before adding it, I ask which explanations it can distinguish, whether a simpler method would work, and whether we can process the data properly.
If those answers are unclear, I tend to leave it out. The team needs sufficient evidence for the current decision; extra charts may only create extra preparation.