I have one following a slight flesh wound, I have the GPS messenger version, which only needs the GPS satellites to work, £2 per week for the subscription service. battery life is very good- you only need to turn it on to "report in" - mine is still on the original batteries (I carry a spare set also). It also has a custom message button that you programme via the website- mine is set to say "no phone signal here, everything okay, will call you later on"- this can be sent to a number of recipients via email and text
Signal reception is very good, turn on get signal and send message within a couple of mins
the Garmin system is good, but I relies on a smartphone to do the reporting thing- not massively reliable in terms of batteries etc.
I think there is a new version coming out- more bells and whistles, but a little cheaper