I have some experience with SPOT devices. In areas where there is good cellular network coverage I would advise against using a SPOT and pick one of the various cellular-based solutions instead. There are a number of reasons for this, but probably the easiest to explain is that the SPOT needs a clear view of the sky to work properly. That means if you land your bird upside-down you've at best got a dot on your map that's several minutes old. A lot can happen in a couple of minutes. Cellular solutions aren't necessarily confined in that manner.
If you're flying in remote areas without cellular coverage, it's probably your best option, but with the same limitation.