The regular NuCalm discs activate the GABAergic system - they are programmed with the signaling of GABA and L-Theanine; the NuCalm PRO discs are programmed with the same, plus the signaling to stimulate the vagus nerve, which connects the brain to vital organs. Stimulating the vagus nerve induces a deeper parasympathetic response.
The regular discs are $2 each. The PRO discs are $4 each. If you're using NuCalm four (4) times a week, the 100 discs that come with the system will last you 6 months. Then, you'll spend another $200 or $400 for the next 6 months.