I have quite a bit of experience with both, and wouldn't recommend either as a primary safety device. PLBs are far better.
SPOT is based on Globalstar, which leaves one without coverage in many areas. I also found it to be incredibly flaky even in areas of allegedly great coverage with a totally open sky.
inReach is vastly more reliable, and with global coverage, so if I was buying one for a (secondary) safety that would be the easy winner of the two. It also has the added benefit of bringing a convenience that PLBs don't, as one can grab weather updates and easily text others for information.
That said, it's not difficult to get into a situation where terrain makes quick satellite acquisition very difficult, and one could wait hours for a message to get out. PLBs are much more reliable in adverse situations (N-S slot canyons), have higher power output than satellite messengers, and are generally built to higher standards. They also don't require a monthly fee.
A legitimate PLB would give one more paths to a swift rescue, especially if SAR aircraft are already up and looking for you.
More info: https://www.backcountrychronicles.com/delorme-satellite-gps-...