3-electrode EEG devices don't really work and that's one of the reasons why biofeedback was a fad of the 1970s. There are some very slick devices out there now like
but at that price it is not going to replace the Polar H10 in my biosignals kit, the respiration radar or the GSR and EMG sensors -- and any of those hidden under coat can tell my phone to tell me that I tilted before I realize it on my own.