The vest is easily vented at the neck, front, and arm holes, and has a drawstring waist that can be left open if desired.
I don't think it breathes well thru the fabric, but it can vent easily.
Regarding insulation value, the Klymit website has a chart on that.
Anecdotally, the vest with air is generally sufficient down to about 20F, and below that temp it is recommended to use the argon gas fill for more insulation value.
I just use the air. I don't have the argon or fill kit.
The advantage is that when you get warm from changing conditions or whatever, you can just let out the air, and reduce insulation value, so you don't get hot. When you slow down or get to camp, you inflate it again with the hand-bulb in the pocket while still wearing it, and it gets warmer.
It's not like a down vest which you have to take off and stow in the pack when you get too warm. When it's deflated, it hangs loosely on the body, and isn't prone to building up heat then.