Does Facial Flex Work?

Only two so-called studies exist on Facial-Flex. Both were written by the same authors, none of whom are doctors. The "studies" were written in 1992 and 1994 and apparently have never been replicated. They were not blinded studies. They were not published in plastic surgical journals. There is a lot to be skeptical of with such "research."
The changes that occur in the face with aging have nothing to due with a lack of exercise of the muscles in the face. Age-related changes are primarily due to deterioration of the structural components of skin (including elastin, collagen, and hyaluronic acid), which lead to sagging, and the loss of subcutaneous volume (such as fat). We correct these with surgery (to lift sagging) and with injectable fillers (to fill volume loss).
In fact, one well proven way to minimize wrinkles is to actually weaken the muscles of the face with agents such as Botox Cosmetic and Dysport. Building up muscle function is very likely the exact opposite of what a patient would want to do.
All the best,
--DCP

I have researched products similar to these as part of my training in aesthetic surgery. Your facial muscles get plenty of exercise in the course of daily life and this device is very unlikely to provide any positive benefit.
This device has been used by plastic surgeons in New York to stretch out the mouth for patients who have had reconstructive surgery and whose mouth openings are too small. This may be its only legitimate use.
Sorry!