Thank you for your feedback!
Last time I taught this course, I asked students whether they felt the rubric was helpful for them. The unanimous answer was yes. Students felt that it helped them understand not only how they were being assessed, but also what skills were included in improving speaking.
The rubric is meant to be an overarching rubric for all speaking tasks. In addition to the rubric, each speaking task has its own individual rubric, with more detailed criteria that assess the skills students need to demonstrate for that task. Let me know if you would like to see an example. I am happy to post one. Specific descriptors such as "no unnatural fillers" are explained and practiced in class lessons.