[mjoxley]

Devices on amazon are repurposed tENS devices which control voltage rather than current. tVNS is an emerging area of research and to repeat studies you need to understand the "dosage" which means the current delivered, because the same voltage can result in different currents depending on resistance. The accuracy of the biphasic waveform is also a factor.

[lvturner]

I checked your bio and this is obviously an area you know a great deal about, and one I'm interested in.

Do you happen to have any high-level resources on the differences, pros & cons of TENS/tVNS/tDCS/PEMF and why one would be chosen over the other?

I'm slowly starting to piece things together, but frankly I'm a bit overwhelmed by it all

[mjoxley]

Thanks. They're all experimental and YMMV. What's exciting with tVNS cf tDCS is that you can use HRV as a measure of efficacy.