Regarding the Netflix code for an extended Gamefly free trial?

I have Netflix, and I’ve enjoyed it very much. So, being a gamer, I would like to give Gamefly a try(Rhyme not intended). Anyways, I heard something about a code in Netflix mailers that allows you an extended trial with Gamefly. The thing is, I can’t find it. Does it appear come every once in a while? Is there a way to get it faster? Is Gamefly even any good?