Do those devices mention whether they expose you to north or south pole energies? If they don't specifically say only the north pole is used then you're getting both energies and that is dangerous. Even it they do say only the north pole is used that may not be accurate, as is the case with some products. The south pole energy should only be used in certain situations by someone who is well schooled in biomagnetics. It can kill you. I'm not claiming to be the expert, but I learned this from reading books by Davis and Rawls, and they are without a doubt the experts.