The VNS device is gammaCore. https://www.gammacore.com/ By itself in typical circumstances, it doesn't work as well as an optimized O2 system. It supposedly has some effect when used as a preventive. I think you have to have a prescription to get it. Previously, and maybe still today, the first month was free but then $598/month after that, in the US.
A 2021 evaluation within the UK National Health Service (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8611122/#:~:text=gammaCore reduces the frequency and,in the first 3 months.) "recommends routine adoption of gammaCore into the UK national health service," but presents these "key points for decision makers":
gammaCore reduces the frequency and severity of cluster headaches but does not work for everyone.
There is currently no evidence of a sustained long-term benefit. Treatment with gammaCore should therefore be stopped if patients do not experience any reduction in symptoms in the first 3 months.
gammaCore was used alongside standard treatment, so decision makers should be aware that the possible benefits achieved with gammaCore are as a result of the addition of gammaCore to current standard treatment.