WS-F5521 or WS-X5530-E2

[Rick Holden]

Could someone please explain to me the difference between these to cards.   WS-F5521 and WS-X5530-E2 I looked on Cisco's web site but still can't get a clear picture of what the difference is. They both seem to be supervisor card with NFFC, but the WS-F5521 card is alot less expensive. Why should I by the WS-X5530-E2 when the other is less then half the price. Thanks.