@Eliot Quick reply - I would purchase the InReach Mini over the Spot.
I have not owned the mini - I own the larger InReach device so I can't speak to the interface but even with my larger InReach, it is much easier to utilize the device through the bluetooth integration to my phone. Keep this in mind because using the device for an extended trip requires a back up battery and a cell phone (on airplane mode though).
I'll share my experiences - I hiked the JMT (240 miles) in 2017 with my Garmin InReach and it performed very well and provided 2 way communications along the entire route. I had a few other hikers that were on the trail with me utilizing a Spot device. They could not communicate with their device to/from their families and only had preset messages to use on the rare occasions it worked. Instead, they asked to use my Garmin to check in with their families in England. The experience they had with that device keeps me from advising anyone to consider that device especially when compared with the very positive experience I had with my Garmin.
I continue to use my Garmin InReach for dayhikes and even in my car if I am on a trip where I will be traveling in an area with little cell service. As a trained wilderness first aid provider, I consider carrying the InReach to be essential.
Good on you for considering this purchase - I think it is a fundamental backcountry tool.
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