Anyone have opinions about charging your loan (mortgage/auto/student) payment using chargesmart.com? I am looking for an MC or Discover card that will earn rewards at 3x or more per dollar spent for a generic category. Even at 3x, the rewards appear to be expensive due to the website charging 2.29% plus $5 transaction fee.

Their blog mentions they are working to add AMEX. If AMEX was added to their network, what card would earn 3x or more rewards for this type of purchase?

Thoughts? Feelings? Please share your experiences with this website. Thanks in advance.