We were on the Preziosa a few weeks ago and like bac513, it was pretty much a waste of money. It worked here and there, and was really only good for messaging.
A little tip - for the Norwegian Fjord cruise we were on recently, 3/4/5G worked for the majority of the trip, with a few exceptions of a couple of hours here and there. I think most of us in the EEA have decent roaming allowances, so once you're not going crazy streaming, your personal package should be more than ample.