There are some limitations on locations for the beta testing, but long term the goal is worldwide. As the community submits their sonar logs for certain areas to Navionics, they make updates to maps with any new information.
gettinthere - the Navionics charts would be different from the base maps in the Garmin system. The SonarCharts for Garmin have one foot contours for coastal areas out to 80 feet, 3 foot contours to 250 feet, and 6 foot contours beyond that. As more and more sonar logs are submitted, the maps get better and better, but it's unfortunate to hear about that catamaran. As with any routing software, users should always double check depths around an automatically generated route, but I'll bring the incident up to the team and see if anyone has heard of the incident and see if the charts have been updated for that area.