At sea, you won't be able to use a mifi. The signal will be whatever the ship carrier is (usually $3 or $4 per minute - my line uses ATT) OR the ship satellite.
A smartphone with 3g/4g (like an iPhone with Facetime and Skype installed) is another good option
I remember researching the 2372 and I'm pretty sure it only works on North American HSPA networks. If you're going Cunard/P&O?, I'm assuming you'll see more European ports? If you think you're going to be on ships for a while, you might want to look at 4G/LTE as it's faster . . . and I think many of the devices may be backwards compatible with 3g networks.
Google "mifi forums" and you can probably learn a bit more . . .