We have been happy with the SPOT device.  It was my fault that ST didn't get the messages, apparently when I added another recipient on my account it cancelled his link.  A double check while still at home would have solved that ahead of time.
The SPOT has been reliable in sending its signals for us.  Sometimes it takes a while for it to locate a satellite.  I set it out in the open at the shoreline of our campsite or on top of my packs while I am paddling.  I have found it works best if lined up to broadcast to the southern sky.  It will signal you when it has been able to send a message.  I generally use the "okay" check-in feature.  Tracking is nice too, but sends a signal every 10 minutes and ends up putting a lot of e-mails on one's account over the course of a few hours.
From looking at the map of where we have been vs the signal locations I can tell it is right on for location information.  The folks at home seem to really enjoy being able to see where we are at any given morning or evening.  The security of being able to send a signal for help if you need it, is nice for the camper.  Account cost for one year is about $100.00.
At times you would like the option of explaining why you need help, etc. and there is no option for that...yet.  A sat phone would allow detailed communication.