This card is only useful for the sign up bonus, other than that, I would suggest using a card that earns 4mpd. However, there are some credit as to why this card might be useful.
Miles earned on this card will be directly credited into your Krisflyer account
1,500 KrisFlyer miles each, for the first two approved Supplementary Cards
From time to time there are some promo tied to the card that will allow you to get the best out of your $ and earn some miles
Amex customer service is really awesome!
An Amex general spending card limits your use (Not all merchant accepts Amex)
Low mile rate
If you plan to get this card, its' best to monitor the sign up bonus before applying. Once you hit the bonus, sock drawer this card!