If you are doing a cruise and it's your first one, I would highly recommend it. We always get at least the 10 picture digital package for cruises. Although CMs gladly take pictures when characters are present, on the cruise, the professional photographers are not CMs, and they are not allowed to touch your camera. There are several opportunities to get family portraits with different backdrops and you would not be able to do this with your own camera.
About MM, I'm always on the fence about it since I always carry my camera. Since CMs gladly take a picture, I will always compare and typically the ones with my camera taken by them are as good or even better than theirs. This year Xmas trip I'll probably get it however and leave my DSLR at home.