Another good reason not to give up the Garmin just yet is having two-way communication on your emergency beacon too. It's not really confirmed or known what Apple is offering here and if there will be any way to communicate with rescuers if you have to initiate a rescue.
With Garmin devices you can text both ways and it has been shown in many rescues to be a huge advantage at getting the right search and rescue or other team to you faster--they can find out what the situation is and if they need to skip right to a helicopter rescue for example. If I were an avid hiker I wouldn't ditch the Garmin just yet (but hopefully in a year or two we'll see if Apple and others try to compete in the satellite rescue beacon world and offer comparable features).
It's two way but predefined messages only. This way apple Apple has a map of messages to some minimal bit value and saves on bandwidth. Garmin InReach allows for predefined messaging too and custom as a pay per message option, it can take 10 minutes or more to send a custom InReach message. Also, InReach uses iridium satellite network which has true global coverage whilst Apple is using Globalstar, which doesn't.
The more I read about the new functionality the more it seems you not only send predefined messages to start the conversation with emergency services but you can send arbitrary text as well.
Inreach is awesome for general communication, coordination for non-emergency where there is no cell reception. I've used it at ski resorts and national parks to meet up with people.
Don't forget you'll likely have your iPhone out a lot when taking photos etc, which means it's at greater risk of being lost or damaged or the battery running out, rendering the satellite features useless. Having a Garmin in your pocket that you never take out has its advantages therefore.
With Garmin devices you can text both ways and it has been shown in many rescues to be a huge advantage at getting the right search and rescue or other team to you faster--they can find out what the situation is and if they need to skip right to a helicopter rescue for example. If I were an avid hiker I wouldn't ditch the Garmin just yet (but hopefully in a year or two we'll see if Apple and others try to compete in the satellite rescue beacon world and offer comparable features).