I got 3 different quotations, can get some comments from sifus here....

material and design not much different, mild steel, simple pattern, house with lots of windows and sliding doors

Quotn #1 - 7200 - saw the sample, finishing is good, smooth and nice paint, joints are even
supplier say he will use the only 'certified' way to install - by drilling hole thru the side of the grill and fixing into wall with screw. Screws cannot be seen so very safe.

Qoutn #2 - 5400 - workmanship is a bit poor, paint is uneven, got thick and thin patches, welding at joints look rough, got blobs of metals. Seen the 'show' house - grill installed by welding little metal 'ears' to the frame and screw onto wall. Screws can be easily seen and accessed. I estimate with a portable power screwdriver, < 3 minutes to open the 2x2 grill for toilet window (4 screws). Other windows more difficult, have to pry open the glass window first.
When I asked, supplier say no problem one. To break in the thief will not bother to unscrew. They use crowbar/carjack to break open or just cut the bars, much easier for them

Quotn #3 - 4800 - finishing a bit poor like in #2. Supplier say he will use a combination of screws and directly welding to the window/door metal frame to install. Got such thing one? I would imagine it will look real horrible with all the welding marks. But he claim will paint over, and this is the safest method. No way can unscrew or jack.

Will like to go for #1, but big price difference due to method of installing. A cursory check around the neighborhood, seems most houses use #2 method to install their grills. Never seen something like #3.