CO2 is cut by 27% through a combination of systems. I think the MALS (air bubble) tech on it's own increases fuel efficiency by ~10%, based on the published papers, and you spend 2% of that gain on actually producing the bubbles.

Apparently break-even on the upgrade cost is reached within a couple months. They are also starting to put it in cruise liners [1].

[1] - http://www.seatrade-insider.com/news/news-headlines/micro-bu...