Thanks for the link! Now I know what I asking Santa for Christmas next year
The Wild Divine sensors are almost entirely thick plastic and go on three fingers. The two sensors that measure galvanic skin response have tiny glass squares in them and the one sensor that measures heart rate variability has a small round metal sensor. I don't know if it's made of nickel or not but I can tell you that the sensors are extremely comfortable. You could call Wild Divine and ask them about the nickel. They have pretty good customer service.
Wild Divine is very sensitive and is an excellent training tool. Hopefully, this new swing towards EEG-based interfaces will prompt the wild divine folks to finally expand their system to include brain-based interactions.
The biggest drawback for me has always been the fact that it's coyingly New Age to the point of being annoying, but this is a matter of personal taste. It was a big investment for me but I wasn't sorry I did it.