Analytical Professor is right, normal grilles can be cut easily. A knowledgeable Malaysian friend once told me that even iron grilles were being cut. He advised to install grilles from professional security company, because their grilles are specially design to prevent break-in from cutting or ripping and bending with crowbar. They use the right material which had gone thru stress test. Why install a normal grille which doesn't do the job of preventing break-in and put your family in danger of break-in by armed robbers?
Another thing is, never place your safety in the hands of security guards, not even the police. What I mean is that you Must do your own part to install all security features. Criminals look for the easiest target, so don't be one.
The Adda heights case clearly stated that the robbers' first target was his Singaporean neighbour's house but couldn't break the locks, thus changing their target to his house. He would definitely not be the victim that night if his house was fully secured with 'security' grilles and other home protection systems.
Don't be the easy target.