Very cool option for someone who is already using it. At end of the day, it still requires a monthly subscription plan in addition to the cost of the product and it also requires recharging. The first is more of a dealbreaker for me. I say that as someone who can get a significant discount on the product itself. I didn’t and chose to go with a PLB instead. In addition, it doesn’t use the same government satellite network that is COPSAS-SARSAT; it uses a commercial set of satellites and a different way of relaying the need for help (GEOS who contacts SAR hence your monthly fee) vs direct to SAR government entity. Different frequencies, which a PLB actually can penetrate better for transmission based on questionable terrain though in the middle of the ocean is not an issue. Lastly, and as you mentioned, waterproofing on the Garmin InReach Mini is only IPX7 which is “Withstands incidental exposure to water of up to 1 meter for up to 30 minutes”. I work in the outdoor industry and some of that is loosely defined meaning it can vary depending on conditions. It also doesn’t float. You will have to remove it from the case for SOS and hope you don’t drop it (oops) and have to keep it out of the water so it doesn’t exceed the time.
I have a floating PLB. ACR PLB 425 view. It is officially waterproof to 16.40 ft (5m) @ 1 hr., 33 ft (10m) @ 10 min.
Some reading:
How to Choose a Personal Locator Beacon or Satellite Messenger | OutdoorGearLab
ACR PLB vs InReach - Backpacking Light
Personal Locator Beacons vs. Iridium Satellite Communicators | Sporty's Pilot Report Articles - from Sporty's Pilot Shop