Overall, this app does not work as well as the other devices in our Personal Locator Beacon review. It is intended to help keep track of family and friends in urban environments with great cell coverage. That said, in certain situations, it could work as well or better than a SEND device (Spot Gen3). We have been in situations where a solid 3G signal can be had on our smartphone, but no satellite signal can be found. Therefor, we recommend using this, or a service like it, in conjunction with a SAT messenger.
If you don't have an iPhone, you can use a similar Find My Friends! app for Android. Strava also offers a similar service to paying members.