We use it in most of our aircraft, it's a great system - had a few false alerts when it was first installed with people forgetting to deactivate it after their flight, but now that everyone's a bit more familiar with it, it's proving to be a helpful system.
It really does have one big advantage over the ELT, in that as the original reply mentioned, it constantly tracks your position so even if the unit is completely destroyed in a crash, or in an area where radio reception may not be great, you still get a pretty good indication of the aircraft's last known position.
It also has a "mark" function which allows you to put a marker on a point of interest which you can then review on the website after the flight - very useful for keeping track of good potential forced landing sites and so forth!