An interactive open-source calculus textbook is compared to a popular commercial textbook. Structured as a non-inferiority study, use of the open-source textbook does not harm student outcomes, and there is evidence that the open-source textbook is better than the commercial textbook in promoting post-course enjoyment of mathematics and confidence in mathematical ability. The open-source textbook is viewed to be more readable as well. Given that open-source textbooks are more affordable, better aligned with the values of academia, and may result in similar student outcomes, committees tasked with deciding which textbook to adopt should consider this open-source textbook.