One source listed is Handbook of Augmentative and Alternative Communication by Denise C. DeCoste. This source talks about ways people can communicate if they have trouble speaking. It explains that assistive communication tools can be simple, like picture boards, or more advanced, like devices that speak for the user. A key detail is that these tools can be changed to fit each person’s needs, which shows that assistive technology is made to help people in different ways depending on what they need.

I don't understand this concept of "we won't include people who are actually in need of the product". I feel like you need opinions of that group to first of all cater to their needs and what they struggle with, they can also exactly point out what works and what doesn't. there is this company that designs for people with limited mobility and since they interegate actual feedback and have the group they cater for in the team, they can come up with solution for mostly every problem the consumer can