As a tech I wonder how the current is induced in the blood stream and the potential for electrocuting yourself. Does it work via inducing a current by magnetic field around a blood vessel. If so, wouldn't you have to have a good idea about the resistance of skin layers, muscles, blood vessels, and bones... I imagine that'd vary greatly depending on genetic factors, weight, musculature, etc. Maybe that's what the potentiometer is for.
Or maybe it runs a blood infusion process thingy ... applying the current between 2 electrodes (probably a lot easier to apply a predictable and consistent value here) as the blood passes out of the body and back in. This would probably be harder to do at home though, since not many of us can use a catheter.
120mA isn't a lot of current... but it doesn't take much to throw your heart off. I haven't a clue how conductive blood is... but could be interesting. But then, if you've got aids... why the hell not?