Arnaud Delorme PhD. uses the Muse Headband:

The Meditation Research Institute Switzerland (MRIS) uses an OpenBCI Headband :

OpenBCI Cyton Headband with 8 Channels for Meditators for 444 USD

No, no, we are only joking.

But are there no other generally accepted and affordable EEG devices used by meditation researchers? According to our findings, there are other affordable EEG devices for mediation researchers available, but we need to develop them ourselves.