today

People have discovered again that these devices are now relatively easy and inexpensive to make and compact as well. Apparently they sell very well too with a good markup.

IMO: Biofeedback devices certainly can be used to keep you calm, and can probably be better to use than the usual kidney and liver-destroying drugs that the average doctor will supply you with for his own profit. The future may lie with further and more complex uses of biofeedback and there could be an opportunity for inventor profit there,