This is a neat concept that packages some smart technology in a very small form factor. Very cool - but as a core benefit, it simply functions to reduce the bulk of your wallet.
Unfortunately the transaction method is limited to the magnetic swipe and it doesn't incorporate pay and wave contactless payment technology.
Ideally, I don't want to carry any cards around. I'd prefer to use my phone. This is what Google wallet is trying to achieve, but in the mean time the Coin card is a good intermediary step as consumers accept the end of plastic.