Is there any value in a post user testing questionnaire considering the sample sizes being small?

I worked at company that after user testing sessions got users to complete a post testing questionnaire. The questionnaire tended to ask user for an NPS score, answer SUS (usability) questions and the user to pick descriptive terms from the Microsoft desirability tool kit.

Considering that most user testing session have a total of 5 to 7 users is there any value in this approach? And how might we benchmark prototypes and early design against quantitative numbers, with any confidence before it goes through costly development?