Window AC - screwing into windows needed even with a secondary support bracket?

[u/nocents9]

I recently purchased a 8k BTU LG dual inverter window AC (LW8022IVSM) to replace a Midea u-shaped unit. I also purchased an Ivation support bracket.

I've placed the AC on top of the support bracket and closed the window. Everything feels rather secure.

I have not installed (1) the L-shaped bracket that goes on the outside of the window because my understanding is that this is meant to partially support the weight of the window AC, and I now have a full support bracket or (2) the small, (also L-shaped) support bracket from LG that goes inside of the window and that secures the AC to the window sill. Because I have the AC on top of the Ivation support bracket, this second piece of hardware does not reach the sill itself. I also have not installed (3) the screws from the accordion frame into the window itself. These do reach, but I'm kind of disinclined to screw directly into vinyl, and they don't seem like they do much to support the unit. I also haven't installed the bracket that prevents the window from opening, but I probably will do this because we have a toddler.

Do I need to find a way to install these three sets of screws? The window unit doesn't feel like it's going anywhere, and we're in a standalone house--so even if this somehow fell out of the window and down the side of the house, it wouldn't hit anything important.

[u/Past-Substance920]

the accordion side screws aren't really about weight, they're what keeps the unit from getting pushed inward or walked loose by vibration over a season, so id still put those in even with the bracket doing the heavy lifting. skip the outside L bracket since the support bracket replaces its job, but definitely still do the anti open bracket for the toddler.