I make my own devices and such quite often and to be SURE they're safe (electrical stimulators) I dial them up to 3x the powr that would be rated as Maximum for them and test such on myself.
Takes a fair amount of dedication to do that to the middle of the sole of one's foot.
Worth it, the safety of my girls comes ahead of everything else, and if something inflicts no physical/neurological harm at those Test settings, then I can be sure they're triply safe at the downrated power levels.