On most of these fun cruises, these are priced to entice. Usually it's a new ship sailing over early from Europe, having some free time, and, visits cities, before it sails to it's home port. I have done a few.
If this is the case here, some of the crew will be newbies on that ship,and you might notice a tad, but, as always the crew is there to please and they do a great job at it. Most of the crew will have been pulled from other ships.
If indeed the price of the one you speak of, is close to a longer cruise, then go for the longer one. If this is a great deal, go and enjoy.....Circles can be a good thing, but really not the case