As a student who has had various studio classes that included necessary critiques on each other's projects, some of the fundamentals I would review/comment on are how well the product works, what is the interaction with the product like, is it eye-catching to buy more, and what I would improve based on my experience.

I would talk about the smell, texture, what is my hair type, how consistent I was, and the results. I feel that these things are important information for the companies and other customers to know so that they can have a good foundation or understanding of how the product is doing.