GigSky may be an even better deal, if you have an unlocked phone. And if you have an older phone lying around, you can get that one unlocked by the carrier and hotspot off it (yes, GigSky allows hot-spotting so you don't need multiple accounts if more than one of you).
https://www.gigsky.com/data-cruises

What I don't understand is why the cruise lines allow these new plans, which seriously undermine their onboard wifi profit center. I believe all of the new connectivity-at-sea options that work through your phone (not through a satellite receiver) use the ship's "cellular at sea" GSM connection.