I would add to this, that in addition to being visible on FR24 / Glidernet, I think the most important feature is the Search and Rescue capabilty.
OGN runs a database which records registered devices for a period of up to 24 hours, so in the unlikely event you go missing for whatever reason, your ID can be looked up in the SAR database and your last known movements can be obtained.
I must admit, I have thought about the idea of having a PANIC button, which sends a new message over P3I indicating you are in trouble, this seems very useful in conjunction with the SAR facility in alerting any listening stations, or the central server.
Thx
Lee