I've been using one for about 2.5 years now and have had no issues with it.
I went with the Spot X because of the built-in keyboard (I didn't get the Bluetooth enabled version). My perspective on it was that in an actual emergency situation, I don't want to be reliant on my cell phone working, too (many satellite trackers have/need a connection to a cell phone for more advanced messaging), and I wanted the ability to have two-way communication with emergency services (the basic Spot tracker is "send a message only"). So for my $0.02, the basic Spot X was the way to go.