I originally owned a Spot and when I bought my first inReach, I did some side by side testing with the devices. I made several trips (different days) on a 10 K loop with both devices tracking my location. The area has some wide open spaces and some very heavy tree cover, so a pretty good test area. I also carried a Garmin GPS to provide a detailed breadcrumb track that I could compare the other devices to.
The Spot never managed a complete track. The best it could do was 2/3 of the trail. The inReach made a complete track 2 out of three times. It only missed one point on the loop that caused it to lose tracking (10 minute interval). The Garmin track didn't have any glitches.
The most disturbing thing that I noticed was that the Spot actually did send the missed points when it reconnected with the satellites, but it sent all missed coordinates to my "current" location (stacked them). This is really disturbing! This is a software issue (what to do with unsent points).
So when you evaluate the accuracy of one of these devices you have to remember that you are evaluating many variables, the most important being the devices ability to connect to the communication satellites, the devices ability to acquire a GPS lock, and what the programmers do with the information that is gathered (software reliability).
Since going from the SE to the Explorer, I've been impressed with the GPS tracks that it captures and I'm satisfied that I can now leave my Garmin at home.