Technology concept prototypes are built to demonstrate a new technical concept or idea. Typically these prototypes focus on some specific technical detail(s). and therefore issues such as industrial design, usability and robustness are not so important.
User study prototypes normally aim to test the business idea or technical concept with end customers. It is at this stage that the industrial design, weight, usability and user interface are critical issues.
Prototypes to showcase to investors typically the initial discussions with external investors are done based on presentations. However,, having a functional prototype makes the message clearer and gives the investor an emotional connection to the product. Due to a limited budget these prototypes typically have limited technology and user features.
R&D prototypes are developed according to the product development process. They typically verify certain phases of the R&D milestones and are not presented outside the organisation. However, with careful design these prototypes may be valuable assets for marketing.