--a rather advanced one from Empi, actually--that comes with connections for four electrode pads and is highly programmable; one can set each electrode in intensity form 1 to 36, and pick from 12 different pulsing patterns.

I originally got it for use with the meralgia parasthetica for my right thigh, but have used it all over my body, especially lately with the right hand radiculopathy based symptoms (still awaiting results on my most recent cervical spine MRI to check for how far the foramen have narrowed and how much nerve root compression is involved, BTW).

I find that the TENS unit works well to block the pain and other parasthetic snesations while it is on--the effect doesn't last very long after I shut it off and remove the electrodes. As I understand it, the reason this works is that pain sensations (as counterintuitive as this may seem) are conducted along the small fiber nerves more slowly than any other type of sensation (due at least in part to the fact that those nerves are typically unmyelinated--myelin speeds nerve impulses), and adding electrical/vibratory sensation to the area interferes with the perception of pain, as those vibratory sensations are conducted to the brain at a much faster rate, and are preferentially perceived.