I have used mine (not mine personally, but from work) in several environments now and have had no problems getting a message out. Return messages take a while sometimes. I have had it int the mountains of New Hampshire, scrub land in Texas, Linville Gorge in North Carolina and in some large cities. I have had no problems getting a location from it. I generally check it myself or have someone else checking my progress. I am using it with the Delorme Pn-60W GPS. I have deliberately tried to mask it with major terrain to the South of me, and no problems. That was the issue with the SPOT.

Both the In-Reach and the GPS unit use only lithium batteries though, but they do last a decent amount of time.