Sounds a lot better than the traditional "space" blanket.
However, it claims to have about 3/4 of the thermal resistance of a in-home winter bed quilt, or about 2.25x the warmth of a in-home SUMMER bed quilt.
Don't know about anyone else, but, for me personally, neither of these measures of comparison mean that, alone, it is going to keep me warm below 50F-55F (which my BR was when i heated with a coal stove located in the Den; BR was furthest fr/the stove) if i'm wearing flannel winter bed clothes, down sleep socks, and a beanie. Think about sleeping in your bed at 50F (probably a tad colder than most keep their bedrooms). Now, remember the matress is providing some underbody insulation. Also, remember "sleeping", so no activity to add warmth.
I just can't picture myself using my winter bed quilt on top of my hiking clothes and Cocoon pullover and keeping my self warm at some point below 40F, and this has only 3/4 the warmth of my winter bed quilt (2/3 the warmth if i use the independent Laboratory's test results and NOT the Mfr's test results).
Forget the reflective nature (the air the product traps is more significant in providing warmth), The reflectivity, IMHO, essentially does nothing as radiative heat loss at body temp is very minimal compared to convection, conduction, and evaporation (if not wearing VBC).
Here's what their website says: "As a rough guide, if you are wearing the type of clothes appropriate for the season and you make some effort to find a sheltered spot and put some insulation underneath you, then in spring, summer and autumn you should be warm and comfortable. In winter you may not be so comfortable, but you should be able to survive for several days in all but the most extreme conditions."
Did anyone notice the words "so comfortable"? Now, there's an understatement, IMHO! THIS IS A JOB FOR....
Please correct me if you think i'm wrong, but sounds to me like MOST of the warmth is coming from the clothes being worn, the underbody insulation, not to mention lack of convective heat loss due to the wind sheltered bivouac site.
I'm just guessing, at some point below 40F nighttime temps (how much below? don't know. RN, your turn, i'm sure that you have some examples/numbers), survival isn't possible due to hypothermia.
Their concept of summer & winter though, might be skewed by their UK winters - a bit different, i'm guessing (UK participants, please help me out here), than northern US & CAN winters, in several respects.
Having said all this, i'll have to check the cost, as i may purchase one, but i don't expect it to keep me alive in the winter w/only my clothes+Cocoon and w/o a sleeping bag.