I had never heard of these but obviously they work well.
A few years ago my daughter had a student in her class of special needs that needed something for his hands to touch to relieve stress so I made several small stuffed "coins" in different fabrics for him to feel so he stayed calm. They were very texturally different, made from velvet, satin, fleece, corduroy,etc. He could keep them in his pocket. She said it helped.