Is there research supporting Quell's efficacy?

Transcutaneous Electrical Nerve Stimulation (TENS) devices have been used by physicians, physical therapists, and other health care professions for decades to manage pain, and are recommended for treatment of chronic pain by the American Society of Anesthesiologists in their practice guidelines. TENS devices like Quell stimulate sensory nerves in your leg with safe, painless, and precise electrical impulses to trigger a natural pain relief response.