According to the advertisement the use of electronic muscle stimulator is both for professional and amateur athletes.
I've never seen one of the topathletes in my town use it, but I've seen the muscle stimulators used by people recovering from a serious accident.
To firm their legmuscles without walking the muscle stimulator was the best equipment available.
The small shocks cause the muscle to contract and relax and this increases bloodflow and thus a much faster recovery, and it also strengthens the muscle.
In the past people recovering from a serious injury needed a lot of extra time because the muscle decayed partly during the healing process. This can be prevented now.
Professional and amateur sporters also use a muscle stimulator after a hard work out session to feel fit again a lot sooner.