I don't know anything about Shimmer, so I don't know how well they fit the mold, but as I understand ADHD Coaching: The general idea is that the coaches are there to supplement therapy and/or drugs with practical "in the weeds" advice. A Therapist would worry about making you feel better, and might point you in the direction of some resources to learn practical coping skills. A coach is one of the resources to help you learn practical skills.