The practical idea
The useful question behind “return on cognitive spend” is whether a tool helps with a real task. You can investigate that question without treating the phrase as a validated educational or financial metric.
Choose a fair comparison
Use a short task with a result you can assess, such as explaining a concept or organizing notes. Agree on the criteria before starting. Allow for differences in difficulty and previous experience.
Record more than speed
Note whether the result was accurate, how much checking it needed, and whether the learner could explain it afterward. Faster completion alone does not show better learning.
Write a modest conclusion
Describe what happened in this attempt and what you would try next. One exercise cannot establish a general advantage, forecast a career, or replace an education or savings plan.