Sent you a PM, but here are my two cents worth. We live in the Seattle area, and have been testing out the Lifeline for about a month. My feeling is that, if you are diving in remote or high current areas it is a great safety addition. Here are some comments from using the unit.
First, purchase the optional $30 pouch. It has several methods for attaching the Lifeline, and will help protect it. I mounted mine on my BCD's waist strap, which locks over my cummerbund.
Second, the instructions for squelch and channel changing are a bit complicated, so I have written them on the outside of the case for easier recall.
Third, I dive with a Garmin wrist GPS unit, so I rely on this more for GPS coordinates, setting waypoints, and tracking trips on Google Earth when back home. The Lifeline also does this, but I don't think it is as smooth as the Garmin unit, which also charges much more rapidly.
Lastly, since radio is line of sight, swells and other obstructions can substantially reduce the reception range. There is a good write up about a group diving off Dominica who surfaced in a squall, could not find their boat, and used the Lifeline to contact another boat who picked them up and returned them to the Island.
So I give it a good score, and will be taking it with me on high current dives in our area, as well as overseas trips.