I used it for a couple of years on a Lowrance MFD even though Lowrance didn't support Alaska weather forecast zones and even refused to add them. I now have it on a Garmin 4212 and the jury is still out but it is not looking good. I have been working with Garmin, Sirius, and WSI over the last 18 months on a problem in how they present sea conditions and winds in southeast Alaska. The forecast will be for 30 knots and they are showing 10 knot wind barbs albeit from the right direction. They are not only wrong, they are really wrong. According to Sirius they found an error in how they were presenting the data but they weren't sure it was their problem, Garmin's problem, or possibly WSI which is the source of their data. (Last fall WSI said they had a problem.)
Another problem I have identified is that Marine Forecasts seem to be missed quite frequently or are being delayed. All other weather data is updated regularly. While the Marine Forecasts are updated every 12 hours, I have gone 18-20 hours before I get an update. Sirius and Garmin are not working on that one yet. They are still trying to solve the first one. The final problem I found with the help of Sirius is that Garmin was not displaying all the weather observation locations reported by NOAA. Garmin only reports real buoys. They don't report unmanned shore locations (Lincoln Rock in Clarence Strait for example) even though Sirius is sending the data. Raymarine MFDs display these locations while Garmin does not.
I don't think there are 5 people in Alaska using Sirius weather. I kind of get the impression I am the only one, otherwise someone would have caught these problems earlier.
Now is it valuable? If it is accurate, yes. If it includes all the weather observations, yes. The surface winds are updated every 3-4 hours so you can see things developing earlier or later than the 12 hour forecast in each of the marine zones. NOAA weather radio coverage in SE Alaska is fair. Trying to listen through an entire broadcast to get two bits of data only to have the station fade out when they get to those two bits is frustrating.
Tom