IMHO, Doug Ritter's "Equipped to Survive" website is a good place to learn about all these gadgets.

I also have the McMurdo Fastfind. I originally bought a PLB to get friends and family (friends were worse than family!) off my back for going out solo. Call it a psychological weight saving, if you want. I am well aware than an injury at my age could, at the very least, end my hiking career, so I'm pretty cautious. Plus at my slow pace I can't keep up with most people. I'm therefore actually less safe hiking with groups because then I push hard to keep up.

I would say that what you get depends on the purpose for which you want it.

If you're only interested in rescue: PLBs use the US Government satellite network which has, of course, far more satellites and better coverage. However, the only time you push the button is for a life-and-death emergency (otherwise you may have several years free board and room in a Federal facility). It is cheaper because there's only the one-time cost (no service contract) and registration (with the US Coast Guard) is free. Yes, you do have to buy a new battery every five years, but by that time there will be new technology (it may even sing and dance to entertain you while you wait for rescue). In other words, assume that you'll probably replace the PLB when the battery warranty is up. I replaced mine sooner because the FastFind was half the weight (and half the price) of the ACR unit I'd been using (I donated the ACR unit to a boy scout troop).

If you also want to keep in touch with family: With a SPOT you can send pre-set messages to the folks back home, which hopefully will keep them from worrying about you. In other words, it's reassurance for your family. You do need to set up the emergency coverage so that their call to confirm your existence (which they do before calling the rescue agency) doesn't go to a family member who's away from their phone. With the second generation SPOT, there appears to be better coverage and fewer lost signals than with the first generation.

While I use a PLB, I really enjoyed following our member BrianLe's hike of the Continental Divide Trail last year and finding his daily location that he sent from his SPOT. I saw his location at the Mexican border before he had a chance to post that he'd finished! I think if I were doing something like that, I might consider the SPOT.

Some of ACR's PLB units now have the ability to send prearranged messsages like the SPOT--for an extra charge, of course. I have not investigated these. The technology is changing really fast!

The best choice (but by far the most expensive) is a satellite phone which allows 2-way communication. The problem with either the PLB or SPOT is that you can't communicate so SAR that knows what to prepare for and so you can get advice/encouragement over the phone.

With any of these gadgets, you may have to wait 24-48 hours (maybe a lot more) for rescue, depending on the availability of rescue personnel, weather conditions, terrain, etc.

I obviously need to test my PLB, too. Thanks, Pika, for the reminder!