I've heard of them, but it is just another flavor of the other on-line sales places. Many trans-Atlantic cruises have bargain basement prices. I saw some deals on other sites where they offered huge onboard credits for the NCL cruises, so perhaps CruiseDeals is offering this credit in the form of a cattle car airline ticket. Or perhaps they have a line on a chartered flight.
You and Dennis are more the world travelers than I am. What does your instincts tell you?