The real important point to keep in mind here is that the Spot and the Delorme are NOT emergency beacons and you should not buy one for that purpose.
Spot and Delorme are neither EPIRB's nor PLB's. Instead they are satelite messenger services intended for convenience not emergency use. Unlike the satelite messengers, the emergency beacons communicate directly with rescue services, have established and predictable battery life, water resistance, etc; and, in addition to initial burst information (ID, GPS coordinates), have additional localized beacons to direct emergency responders when they reach the area. The messenger services provided none of these features.
You can go to the ACR website (or McMurdo or one of the other major players) and read concise descriptions of the differences between EPIRB and PLB - Jack hit the major points.
Here is an article from Soundings:
PLB vs. EPIRB - which is right for you?
and another from Landfall Navigation:
PLB or EPIRB?
Good luck. There is a ton of info on this if you google it. If I were you, I would want to read the source materials in addition to forum opinions.