Seems like the main difference is actually not needing your phone for connectivity. It’ll hurt battery life. Good for emergencies but I doubt Garmin’s software can compete with Apple.
Edit: This would make a great watch for sailors to supplement an EPIRB.
Essentially, Garmin is the product you buy when money is no object. Either because you are obscenely wealthy, or because you are trusting their product with your life and the lives of your passengers. They have some consumer grade stuff too that is usually trickling down from their obscenely expensive other businesses.
On top of that, T-Mobile has sat->cell now even for my iPhone 13. I tried the beta, it gets the job done and pretty seamlessly. It’s a monthly extra, so I’ll keep the InReach for now, but it’s time is limited.