I haven't used one personally, but a good friend of mine has a Mini that he uses when he goes off on his weeks long overland trips out in the SW US. He only activates it for the months he's gone then disables it the rest of the year. He swears by it, as do others I've talked to who do similar things.

I, myself, have gotten myself into enough situations where I would have been very screwed had I actually needed emergency communications (back-woods trails and such where there is no cell service or long-range radio on hand) and the last outing we got into a spot of trouble on a completely iced over forestry trail heading up a mountain that had we NOT managed to (very luckily) get everyone turned around on that trail and very slowly made our way back down the mountain that we would have been in a very bad spot if someone had gone over the side.

So I'm looking at them myself now, both the Mini and the Explorer and I'm leaning to the Explorer just because the mapping would make it more useful to me.