I personally think the Spot is a secondary device. I would go with the PLB or an EPIRB. EPIRB's have come way down in price but then again so have the PLB's.

Don't forget with the Spot you have to subscribe to a service after purchase. So don't forget to factor that in. With the PLB and EPIRB only fee after purchase is to replace batteries on the EPIRB, not sure on the PLB but they may be user replaceable.