Very similar story to your OP, my mom bought me one for a month long trip in AK this summer. I couldn't get the thing to work ever while still at home here in NY before I left, so we were pretty worried we'd gotten a dud.

As soon as I got it away from all the interference and towers near NYC, it worked great for the whole trip in Alaska. We checked in every day so our loved ones knew we were ok. It's not hard to know it's successfully sent, the light stops blinking, and if it's having trouble finding the satellite, it blinks out of sync. Not a tough system, but if I hadn't read and re-read the instructions when I couldn't get it to work while testing it, I wouldn't know.

For us, we brought two extra sets of (lithium obviously, as they stipulate it must be lithium batteries) batteries, and never needed them. Wasted weight, but better than the alternative - getting yelled at because "our faces got eaten by a bear"