It's cheaper, newer, and more popular than PLBs. Also, you can click a button and it will send an "I'm OK" email home. There's an option for active tracking. I'm not trying to sell it, but more people seem to be using these than PLB's now.
Completely on topic as far as I'm concerned, it's specifically targeted at the outdoors and could find uses in a number of activities that people participate in here.
Yes, absolutely! I've seen one in action on the AT and it is an incredible device. I know you can't just start a question to recommend it, but.... ;)
I think the device could apply to more than just hikers/backpackers, so questions about it have a place on this exchange.