I actually write for this company, but didn't know about the challenge until Mike Humphreys bought it to my attention. So thanks go to him.
Biggest company in the Agora, Inc health division. Other copywriters who have written for NewMarket Health are Arthur Johnson, Jim Rutz, Lee Euler and Kent Komae.
So, although there's a high chance you won't get paid squat for your work or even see it tested, reward potential could be massive if you're hungry and talented!