I think it's relatively safe as long as you know the limits–especially when it comes to when and where not to play. Like all other games, it could be a source of distraction and you must always know your levels of priority
I dont think so. I personally tried it recently and it somehow gets too addictive. Kids might be focused on it too much that they will not be aware of their surroundings.
No for me, regardless of age. It is prone to accidents, phone snatching/holdup and the player might even get lost.