True enough, but their web site description includes the phrase "equivalent to a medium-size sleeping bag" which strongly implies some insulation value. Their illustration shows interior baffling which should provide some insulation. At $50, they are priced within the range of some fairly cheap and reasonably warm sleeping bags, like the Slumberjack brand. it will be interesting to see the results of objective valuations, like those often provided by ETS.

Right now, I am not sure I would run right out and buy one. If bulk and weight (such as something carried in a car) were not a consideration, I would go with an inexpensive, synthetic fill bag for roughly the same price.

If this product does provide some insulation value above and beyond that provided by other AMK bivvy products, it might be worth it.

To try and answer JI's question, you can sleep just fine in a bivvy sack, provided you are significantly exercised. Sleeping in a nice, cozy, warm sleeping bag can be as good as it gets.