Amazon Payment for U.S. ?

I notice that opencart amazon payment is for uk/de merchants only. I saw the paid extension for $35 but I'm hesitant. I don't want to pay the money and if it doesn't work.

Has anyone use this extension? http://www.opencart.com/index.php?route ... n_id=12181

One of the comments states that it does not "come to the payment success page" but instead goes to the home page and that it "does not empty the cart". Another (somewhere on opencart forum) states that it kept adding extra shipping?

Has anyone used this extension or is there a better one. I'm in the U.S..

Thanks!