They offered to refund my credit card too. I already have everything settled with the credit card I used so I told them I preferred the OBC. I'm sure I'll have no trouble spending it quickly.
This option is a little risky though, as the OBC's are non-refundable and for that cruise only. They made a point of telling me that. Whereas, the refund is in your pocket so to speak. I think the next time I'll take the refund. I learn something new everyday.