They seem to be 2 diff designs one vertical and one horizontal?
Generally if the grille design doesn't have too many weak spots, they will aim to cut the weakest spot i.e. at the padlock 'ears'.

Your imaginationnon how to cut a grille will be using a hacksaw blade, a car jack, or a hammer/crowbar (usually aim at weaker hinge pins).

From Korean series "To catch a criminal, you have to think like one."

They will likely target the easiest method - your padlock ears.
Noone really cuts and yanks the grille anymore.

Whilst the L shape cover protects the padlock ears from direct access, a padlock with larger shank (e.g. Viro 4143) fills up the holes and covers (encases) more area of the padlock ears as a further deterrent.

3kim hinges better built over the elcheapo grilles. After you install you can walk around and compare

For the same weight, a hollow bar/tube is stronger than a flat bar.
The thickness of material used i.e. 1.2mm over 1.0mm will give some additional protection from bending/yanking; however at the equillibrium point even with best material thickness used also it will just transfer failure point from the hollow bar deformation (like the one in the pic) to the welds of the bars.

With the same material - Longer (vertical design) bars are relatively easier to yank than shorter (horizontal) bars design, due to angular velocity providing lots of leverage with tiny effort.

You may be able to 'cheat' the design approval a little by incorporating more bars than required (ie. More densely located bars than reference design spec); if people fit in 25 bars you fit in 32 bars for the same door size (packing them closer). It adds more time needed to cut and yank back the grille 

The appearance of 1.0mm and 1.2mm are the same.
And thieves don't take longer to cut the 1.2mm than 1.0mm.

The only differences are the sound when you knock on it and possibly slightly more impact resistance.

No need. It will be fine material-wise. The tube structure of hollow section gives more strength against bending as compared to a flat bar of the same mass (weight).

Its more to a deterrent device rather than total bulletproofing like a bank vault door

I used the matte white powder coating (not glossy), no prob Matte look stands out from the typical glossy one that looks like paintjob rather than powder coated..also matte is harder to do

I'm surprise why lowyat forumer keep recommend 3kim
i read the good feedback at forum and decided to let them install grills of my landed house.

However the powder coat start rusty after 2 month installation and the sales girl doesn't respond at all after full payment done.
What a bad service.