I did mine too (3 only)... hahahaha... but the original HDB one really cannot make... I got the round type like Hippo for $50.00... bargain until he gives in. That Uncle quite talkative, just keep talking and the price will go down...
After I install it, I happen to notice that if the thief/robber really knock off your door grill, it's really loud.. unless your whole family is away (*holiday) or got hearing impairment, else you should be awake... next, those doors are not aluminium, its more of hollow cast metal, even if the burgler/thief got to steal it and got it off... it hardly worth any money as the paint is already burn in, recycling warehouse doesn't really consider it as good material.
However, HDB does have it's reason for the simple hinge lock. It will make it easier for you if you want to change your doors the next time round....