The boots we wore during Artic training in Alaska were of a type that could be partially inflated to provide dead-airspace insulation. The "Mickey Mouse" boots were warm down, but you had to change your socks two or three times a day if you wanted dry feet - they held in all your sweat. I can see the same problem with the inflatable vest - warm but a massive moisture barrier with little to no venting. Wouldn't want to be wearing it and doing anything resembling manual labor.

Given how cheap, useful and common fleece is, why not just by a fleece vest?
(Or a fleece jacket, mitts and hat)

Somehow, I doubt it.

The whole point of insulation is to keep the warmth of your body near you. Air isn't the greatest of insulating mediums, since there's problems with radiant heat loss, right, and convection too if you talk about air moving within the garmet. Instead, by wearing clothes of different varieties, we keep the air around us "trapped" and thus slow the rate of heat lost to the environment. I can't envision how changing one gas (ie, air around our body) and wrapping it in another gas (in this case, argon) would help. I wonder if, instead, the jacket material is trapping the heat the same way a plastic bag would.

After all, think about a mountain top, say something in the Rockies. You'd think that being 10'000 feet up, you'd be 2 miles closer to the sun, and a bit warmer, right? Yeah, not happening.

I doubt it, too. Down and fleece work by trapping air so it can't move around as much, which reduces heat loss. Air free to circulate goes from the warm side, absorbs heat, moves to the cold side, and releases the heat to the other size. This is why vacuum bottles are such a great thing - no air means no convection or conduction.

I believe argon has about 2/3 the heat capacity of dry air, so it would be a little better, in the same way steel doesn't conduct heat as well as copper.

All that said, it's a pocket sized thing where a fleece or down vest is not. I knew I saw it somewhere...here's a link for sale, and a review:

http://www.bepreparedtosurvive.com/ProtectionProducts.htm

I have no connection to the site, but have read from someone on here that it's reputable.

I believe this product is focusing on storage space, being small enough so that you would have it in a smaller kit you would actually carry. The combo you suggest would be quite a bit bulkier in your kit. This vest is not the best item to have for hypothermia, but I believe it does meet it's objective. A polypro balaklava with gore-tex hood would be a good addition as would many other things. With all the kits you may envision, you need to choose between bulk, utility and odds of needing that category of gear. This fills a particular nitch, but may not be an item you choose to go with.

Here's another write-up:

http://207.210.105.72/~halcon21/forum/index.php?topic=567.0

You need to make tiny pockets, not just a giant air bubble that allows the air to circulate freely. Like a thermarest ground sheet - it has lots of pores that are filled with air.

Dead air isolates. Allow the air to move and the density differences between warm and cold air will set up a circulation which carries heat away from you.

The US military "Mickey Mouse" boots with the air valve on the side are designed to never open the valve unless in an aircraft. Primarily for a change in pressure. It is recommended that you so not open the valve and certainly do not inflate the boot. The reason is by blowing breath into the boot insulation you introduce moisture which freezes and compromises the insulation. This info comes from the tag on the boot and from the Cold Weather Operations manual. Just a FYI.
I would expect the same results using the air vest, in the right cold conditions you could have a vest of air and ice crystals.