According to most research I found, there seems to be some indication that there is some carryover to strength gains with electrical stimulation.  Basically allowing the muscles to have involuntary muscular contractions through the electrical signals allows for strength gains and/or quicker recovery.  With individuals who had spinal cord injuries, the ES subjects showed about 30% better recovery than those who were in the control group, just an example.  One other aspect I read about though was, like anything else, using the ES too many times will allow the body to become used to the stimulation and for normal machines, there isn't enough power in the current to “overload” to provide adequate recovery.  So I would recommend once a week at the end of your training week for 10 to 15 weeks and then cycle off it for a month or so then retry the procedure.