I was in this business for several years.
Big believer in TENs (transcutaneous electrical neural stim). Wife delivered two babies, naturally, with only TENs for pain control. I've seen it work wonders for people in many ways.
NMEs (neuroelectrical muscle stim) can't hypertrophy or grow muscle. It can be used in an atrophy situation, say post injury or surgery, to help bring a muscle back to normal. Also used to activate a muscle and provide feedback to teach a patient to fire the proper muscle.
Russian stim (burst mode alternating current) was believed to have the ability to hypertrophy muscle. No real empirical evidence to back that up though. I can also state unequivocally that it hurts like a bitch. I've seen it used a lot to fatigue a muscle for folks that have spasticity. Also used by some to fatigue muscles for manual scoliosis treatment techniques.
The whole electro therapy modality industry has fallen apart. Insurances stopped paying, so home use has really waned. Still used, but it's now pretty much over the counter, out of pocket. Physical therapists still use, to good effect, in clinics.
So now you know more than you ever wanted to.