I have not seen any brands hallucinated. The biggest issue was the math as you pointed out. I created an if-then-else if statements in the prompt to force the use of code/Python for calculations.

The free version of Gemini functions less well than the others because it executes my instructions less rigorously, but I have not seen product prevalence over others. I'm also not sure how I could track though without running the same case study several dozen times to see if anything statistically significant comes ups or changes.

At the end of the day I would say my idea is best for getting you from 5% knowledge on a topic to an 80% level and a much more advanced and objective place to make a decision and finish out with your own "eyes-on" research.