Hi falcon5000,
The problem is that nothing else weighing in at around 500 grams is really going to keep your warm either at 40F or 4C, except for perhaps an ultralighweight Down Bag with the very highest specifications.
http://www.phdesigns.co.uk/product_info.php?cPath=25_58&products_id=31Even then it would require the use of a bivi bag designed with breathable materials, which is again another 300-400 grams, when used in conjuction with the sleeping bag in wet conditions and windy conditions. e.g Rab Survival Zone Bivi or Alpkit Hunka bivi
http://www.alpkit.com/hunka/The main problem with the 'Blizzard Bag or Blanket' is the word 'Blizzard'. It claims a Tog rating of 8. This is a comfort temperature equivalent to a 1-2 season sleeping bag i.e. late spring/summer/early autumn. Certainly not a winter 'Blizzard' application product. These products are certainly an improvement on the conventional space or mylar blanket but there needs to be a reality check on its claimed usefulness in winter conditions.
From the Blizzard Survival Website;
A report by the British Royal Marines has proved that Blizzard Survival Bags are up four times more effective in cold weather warfare conditions than current issue UK army survival bags.
The three day trials were conducted in Arctic Norway, at temperatures down to -13°C (8.6°F).
They also showed that our Reflexcell™ material kept soldiers warm up to three times longer than bivvy bags commonly used by civilian mountaineers.
The British Royal Marines are generally issued Snugpack Softie 12 osprey or Discovery 15 Sleeping Bags rated to -12C to -15C weighing in around 1.75 to 2.4 Kg together with a British Army Goretex Bivi bag (800 grams). I don't know what survival bag they are referring to. Your certainly correct about the 'hype' though.
I wouldn't rely on this type of product in temperatures less than 10C to keep myself warm and dry, but then being trussed up like a turkey has no appeal either.
If it was a choice between the army poncho and the 'Blizzard Blanket' in dire circumstances of cold, wet and windy conditions to keep myself from suffering a cold weather injury overnight in an emergency I would have to pick the 'Blizzard Blanket' over the poncho. (especially if the poncho was not made from a vapour permeable material)