I am going to sort of defend the person who posted about the baby leash here. I don't know their intent but I will share something that ran through my head here. Of course, you should do whatever you need to to keep your child safe. Nobody is disputing that. What ran through my mind is that there were some people talking about their 9 and 11 year olds that run off.

Unless those kids are special needs with legitimate issues then sorry, the parent needs to get a little more aggressive in their teachings.
I don't use leashes and am not a fan of them, however, I don't care who uses them. They have their reasons. It is not for me to decide what others do.
As for the GPS- do I think it is a bit over the top? For me, yes. If it makes the OP feel more secure then they should use one. I am sure there are plenty of things I do that people think are over the top too. Everyone has to decide their own comfort level. That being said, whatever method you (a general you) use, I hope it doesn't lead to complacency. Those are aids that do help but don't let it give you a false sense of security.
Good luck with whatever you chose and have a great trip!