Bigfoot,
All true. I have the apps for both the iPad and my Android phone. I download appropriate maps for the area of interest ahead of time and use either app to read, and compose the messages. It's as easy as sending texts by phone. If your device does not have a true GPS chip but uses cell tower to provide location information, the inreach provides that true GPS function for you and the app shows your location on the map.
While it can be very slow to send/receive messages, it is much faster than hiking 20 miles to an area with cell service.
As far as the subscription fee service, get the lowest cost monthly version and pay the 50 cents per message that will seem dirt cheap if you are trying to get help for an injured friend or family member. For me, this is my last chance backup system and I hope to not need it. In most places without cell service, I can reach someone on my ham radio who can summon help for me. In that case, having the inreach provide lat lon is not a bad thing.
Paul