I have always been a little suspicious of relying on Spot as it sometimes misses a position send to the satellite, or even more than one.
Not sure if Spidertracks is better or not.
My Spot unit is set at 5 minute updates (it is the later version that can do more than 10 minutely).
The other issue is unless someone following your progress on Spot on a computer, no one will know you have stopped moving till you are missed in some other way(eg overdue at destination). You could fix this if you are crashed but not totally disabled by injuries buy pressing the SOS button on Spot, if it has a clear view of sky.
Not sure if PLB is better at getting signal out if limited view of sky (ie tree canopy).
So I carry Spot and 406PLB(GPS).
I realise nothing is perfect and Spot or Spidetracks have a valuable place in the defences, but so does 406PLB.