I haven't looked at SPOT recently but 6 months ago Spidertracks was still the better solution for tracking because in case of an emergency you don't need to press any buttons, because you might be unable to do so, and the unit due to it's non movement for x minutes deduces there is a problem and sends an emergency message...
This makes it a passive emergency system if you know what I mean. It's sort of set up and forget.
And no I am not connected with them...