Hi JPaula- I also have used Gammacore and I've had nerve blocks as well. The Gammacore is of course less invasive- though I must say the nerve blocks weren't as dramatic as I feared. Have you ever had Botox?
On Gammacore, Kerrie's articles (to which Joanna has already sent links above) are incredibly instructive and I'm not sure what else I can add except to say that I found it very helpful initially with offsetting my migraine pain, but eventually that efficacy faded- however- what it helps mostly with, for me, is nausea and vomiting. It IMMEDIATELY calms and quiets my nausea. Within 15 seconds of turning it on, I can feel my gut settling. It's quite wonderful in that way for someone like me, who struggles with nausea and vomiting on a more than weekly basis.
It can be difficult to get, and maintain, health insurance coverage for Gammacore at this stage in the game- but if it works for you, it's well worth fighting for.
If you have any specific questions, please let us know!