I've got the original spot, but didn't renew the service. It was OK, but I had a lot of trouble with it tracking in the places where I wanted it to track. It sort of worked, but wasn't as reliable as I hoped. I hear the later models are better. I think there are three common options:
1) spot
- tracking, messaging, oh crap - send SAR
pay for unit, and pay for plan
2) delorme in reach
- tracking, TWO WAY messaging, oh crap
pay for unit, and pay for plan, more expensive than spot, but uses iridium sats, in theory and reportedly, better coverage
3) PLB, the ACR resqlink seems to be a great choice.
- oh crap only, but more likely to succeed in that scenario that the spot/delorme
pay for the unit, no other cost, batteries every five years.
As I primarily ride alone the most important feature for me is to get the help I need (or someone else needs) in dire circumstances. I figure in those circumstances I'm likely to be separated from the bike, may not be able to move very well, and may not be thinking well. For the highest change of success I'm going to go the PLB route, specifically the ACR ResQLink, and keep it in my jacket pocket 100% of the time.
With that covered, I may add a bike mounted spot or delorme at some point, but I consider that a ways down the line in the recreation budget.
There's currently a $50 rebate on the ACR ResQLink, or a bundle of extra goodies if you want them. Net price should be just about $200, or given a five year life, about one less beer a month.
http://www.acrartex.com/products/catalog/personal-locator-beacons/resqlink-plb/