He was one of the most influential theorists of the Late Middle Ages, and was the first to propose an idea which was to transform musical notation permanently: that the duration of any note should be determined by its appearance on the page, and not from context alone.
Unlike many theoretical treatises of the 13th century, it was a practical guide, and entirely avoided metaphysical speculations; it was evidently written for musicians, and was full of musical examples for each point made in the text.
[1] The topics covered in the treatise include organum, discant, polyphony, clausulae, conductus, and indeed all the compositional techniques of the 13th century Notre Dame school.
From the evidence of the spread of his treatise and the writings of later scholars, this innovation seems to have been received well; then again Franco was a papal chaplain and a preceptor of a large body of knights, and the acceptance of the method may have had little to do with democracy.
The De mensurabili musica dates from about 1240, not long before; clearly the mid-13th century was a time of progress in music notation and theory, even if it were only catching up with the current state of composition and performance.