Nowadays people carry thier cell phone with them at all times, so whats your point?
What would be the point of that?
Speaking as a fellow German, I would never share that info with friends, but using that feature with my SO or future kids, sure. Not to spy on them, but e.g. to know they're safe when I expected them to be home already.
There are much more dangers than just the government even if I chose to use the stasi as an example. I just thought that it makes for a good example where you can know a person for years and still get betrayed by them.
To your edit: Especially using this with kids (probably pressured to do so) is icky. You can claim that you are not spying on them, but you are. Maybe for their safety, but safety is often used to remove rights like this. You still spy on them.
I remember my cousin and I got lost in Disneyland once, because we both somehow forgot where the meeting spot was. We didn’t have phones, and we were, of course, fine—truth be told, Disneyland is probably among the safest places to get lost. But it would have been nice if we’d had a tracker that could just tell Dad where we were.
The negative I see here is that it teaches your child that giving up rights for the promise of more safety (or more likely just because an authority figure says so) is something good and normal.
Also teaching that the concept of constant surveillance is good and normal.
I don't understand why you would like to do this just in case or because "it would have been nice".