Given the project is in an early stage with a "rudimentary prototype," a usability review is the most appropriate and efficient approach. This method, also known as an expert review or heuristic evaluation, allows the usability expert to leverage their knowledge to inspect the prototype against established usability principles. It is a cost-effective method that provides rapid, actionable feedback to the development team. This is ideal for early-stage artifacts where formal user-based testing would be premature and less efficient. The established positive relationship with the development team further enhances the effectiveness of this collaborative, expert-driven feedback loop.

B. Unmoderated usability test: This method requires a more stable and functional prototype to allow users to complete tasks independently without real-time guidance.

C. Usability maturity assessment: This evaluates an organization's overall usability processes and capabilities, not the usability of a specific product prototype.

D. Usability test in the lab: This is a formal, resource-intensive method better suited for more mature, interactive prototypes or finished products, not a rudimentary one.

---

1. ISTQB® Certified Tester Foundation Level Usability Testing Syllabus (Version 2018).

Section 2.2.1, Usability Review: "Usability reviews can be applied at any stage of the development lifecycle, from early concepts and prototypes to the finished product... Usability reviews are relatively inexpensive to perform compared to usability tests." This supports using reviews on early prototypes.

Section 2.2.2, Usability Testing: This section describes methods involving end-users (like lab tests), which generally require more mature artifacts and are more resource-intensive than expert reviews.

2. Nielsen, J. (1994). Heuristic evaluation. In J. Nielsen & R. L. Mack (Eds.), Usability inspection methods (pp. 25–62). John Wiley & Sons.

Chapter 2, Heuristic Evaluation: This foundational text establishes heuristic evaluation (a type of usability review) as a "discount usability engineering method." It emphasizes that it is fast, inexpensive, and effective for finding usability problems early in the design process, even with low-fidelity prototypes.

3. Lazar, J., Feng, J. H., & Hochheiser, H. (2017). Research Methods in Human-Computer Interaction (2nd ed.). Morgan Kaufmann.

Chapter 8, Usability Testing: This chapter contrasts expert reviews with user-based testing, noting that "Expert reviews can be useful at any stage of the development process, but they are especially useful at the early stages of design, when it may be too early to get meaningful feedback from users." (p. 201).