I wouldn’t leave any of the water ballast boats in for winter if you often receive prolonged or deep freezing temperatures. (As is the case where I live) The occasional, short cold snap is a different condition. The seal to the ballast tank is often not perfect and often over time allows the tank to fill.
While the bubbler will prevent the water outside the boat from freezing as long as its functioning and not too cold, it will not likely prevent water in the ballast tank from freezing.
As observed in an earlier post the second issue with the water ballast boats is that they are not overly stable with the ballast tank empty.