We do not have many reports about Botox's effect on salivary glands, submandibular glands included. The recent report about Botox use to reduce parotid gland hypertrophy has shown about 10-12% percent volume reduction after several weeks. Repeated injections may be needed to keep glands under...
You may be noticing the counter muscle (vs. the treated muscle) reacting when you make exaggerated facial expressions. As you have not had this issue with Botox or Dysport you may want to remain with those products instead of Juveau.
I encourage you to visit with an expert injector for an evaluation. If the brows are treated incorrectly it can make the brow appear and/or feel heavy. In contrast, when treated correctly Botox can give a more refreshed appearance to the eyes.