You sure can stimulate the vagus, through an implantable device. They are used for seizure prevention in refractory epilepsy, or for refractory major depression that has not responded to ECT. VNS side effects usually include cough and hoarseness. Some get nausea, difficulty swallowing, and paresthesias. Overall the side effect profile is reasonable for the efficacy in refractory epilepsy and depression. What I haven't seen is anyone activating their VNS because it makes them feel super chill, happy, and refreshed.
A lot of research has gone into figuring out how VNS works, and it still is not clear. There is some evidence that it is through thalamocortical and/or hypothalamocortical modulation, through projections from the nucleus tractus solitarius through the raphe nuclei, nucleus ambiguus, parabrachial nucleus, and the adjacent locus coeruleus. VNS increases fos transcription and BDNF levels in the brainstem.
All sorts of complementary medicine strategies are theorized to stimulate the vagus and "release neurotransmitters", things like music therapy, chanting, etc. So it's not clear to me how these earbuds would do anything that others can't already do. Neuromusicology is a real thing, but the emphasis in that branch of research is on the auditory stimuli and the resultant neurologic responses, not which earbuds you use. You can technically stimulate the Vagus through the auricular branch (sometimes called Arnold's nerve), the same way that sticking a feather in your ear (or ice cold water) can make you throw up. It's not at all clear that minimal electrical stimulation that doesn't cause pain in the ear canal would have anywhere close to the same effect as a VNS implanted in the neck.
Electrical stimulation of the vagus in sync with music is interesting in theory, but this company seems to have left out the steps where you demonstrate biological utility of this strategy, and gone straight to the snake oil stage of marketing it. Good for them, there's a sucker born every minute and as long as they aren't marketing it for people with actual medical problems, that's just capitalism I suppose. There is so much suggestion that goes on when you say "here, put these on and it will stimulate your brain and release dopamine". Let's see them take the Pepsi challenge and turn on the electrical stimulation desynchronized from the music in a blinded control group, which per their own theory should stop the perceived benefit, or stimulate the exterior ear instead of the Vagus.
The lay public likes to think of neurotransmitters as good or bad. Chocolate makes you release dopamine! Chocolate = good, therefore dopamine = good! Let's all release more dopamine with these earbuds! In reality, it's the relative distribution of these neurotransmitters resulting from discontinuously firing neurons in positively and negatively influenced neural circuits, all interacting in different areas of the brain, that modulate complex phenotypes like mood and attention. But the emphasis is on modulation, not inducement. You might be able to help yourself achieve a trance-like state by sitting in a quiet room and chanting "Om" to yourself. But shouting "Om" while you're riding a rollercoaster doesn't result in trance. Based on actual science*, vagal nerve stimulation seems to have the biggest neurotransmitter effects on norepinephrine in the prefrontal cortex. But maybe the advertising team wanted to focus on neurotransmitters associated with chill vibes rather than norepi, which might make people think about Mountain Dew.
Why did I spend so much time responding to this?
*Follesa P, Biggio F, Gorini Caria S, Talani G, Dazzi L, et al.: Vagus nerve stimulation increases norepinephrine concentration and the gene expression of BDNF and bFGF in the rat brain. Brain Res 1179:28–34, 2007
