Review (2/5): Awfully sketchy packaging..
Product feels pretty good, and I can feel it is giving my jaw a pretty decent workout. Came packaged in a small zip-lock bag, inside a ring box, that you might use to package cheap jewelry. Sticker on it seemed to indicate that it had been opened. Needless to say, these got a good soak in bleach before entering my mouth.
Update: after about a half of week use I'm starting to see small tears in the rubber. Additionally its beginning to permanently deform. Keep in mind I'm not a person of extraordinary jaw strength.