In thick trees along a steep cliff band in in the Alps, where cell networks are massively more expansive than in the rural U.S., we were able to check our email, make a call, and check to be sure that our buddy Carson was still sitting on his couch in Waialua, Hawaii. And he could have checked his app to see that we were camped out in the trees there, below a massive BASE jump near Chamonix, even if I was unconscious and not able to pick up the phone and dial. Meanwhile, we had no signal on either of the SPOT devices or the Garmin. One thing that became very apparent using the inReach and SPOT devices was that without a very clear view to an open sky, they do not work well at all. A phone well inside a 3G network area, on the other hand, works under cover, indoors, etc.
In another instance, we were backcountry skiing miles south of Kirkwood Ski Resort in California in a 4,000-foot deep canyon. While avalanche danger was not high, it was steep terrain with a good chance of hitting rocks (multiple times) if you lost control. Miraculously, we had good cell coverage. We were in a group, but had this been a solo mission and we had fallen and been badly injured, it would have been easy to find exactly where were were.
While at first we were skeptical and considered not even including it, this is an interesting extra option for people who travel in areas where mobile phone coverage (we're talking solid signal) is plentiful. Clearly, however, this could never be considered as a standalone emergency messaging device. Don't even think about relying on this app for anything other than entertainment and stalking your friends who are willing to go through the setup process.