Staying in 14th Floor, with 3 tier security, didn't bother to install one, my balcony sliding door is one way lock (only can be lock/unlocked inside), so i guess is pretty ok, but I'm the only 1 didn't install grille on the main door.

On the yard area, mine was due the design of the condo, it blocked most of the way for someone to climb in, so didn't install that too.