Our three EEG channels: enough for effective brain training?

Yes. What matters is not how many sensors there are but where they sit and how clean the signal is.

Sens.ai records from three midline sites, Fz, Cz and Pz, placed over the hubs of the brain's rich club network. Three sensors in the right places cover what the majority of training actually needs.

The signal itself is lab-grade: the headset reads and trains from delta through the third harmonic of gamma, 1 Hz to 120 Hz, at up to 1,000 samples per second. Sensor count on its own tells you very little, because a larger array with a noisier signal is not an improvement.