Obviously each situation is different, but I'm very much on the side of trusting kids vs having some kind of leash. Sure, my kids would probably be fine w/ the caveat that I can see whatever they're doing if that means they get a phone, but to me, it also shows that I don't trust them, and that could mean they won't come to me when something I can't track happens. I personally value that two-way trust a lot more than whatever short-term benefits tracking gives me, and I go out of my way to tell my kids what I could do so they know how much I trust them.

So far it has worked out, but my kids aren't teenagers yet (close), so we'll see what happens once their social circle broadens a bit.