This is not the first study I have seen linking Vagus nerve stimulation to a dramatic improvement in mental health. That said, the same results can be achieved through regular abdominal exercises. Crunches, sit-ups, etc, all stimulate the vagus nerve. If you activate your abs regularly, you should achieve the same results as this device.

EDIT: Another link between abdominal work and brain function.

https://www.psypost.org/scientists-discover-a-hydraulic-link-between-the-abdomen-and-the-brain/