The cheaper ones are lighter, which is often what you want when hiking. The Heatsheets Emergency Bivy, around $16, weighs about 4 oz. For #34, the Thermo-Lite weighs close to 7 oz. It is probably a little warmer (I have not yet had to use either of these for real).. The Heatsheets is what I tuck away routinely, and I will bump up to the Thermo-Lite when I can afford the additional weight and conditions might be a bit more severe. I have no experience with the SOL version, but I doubt that it is radically different.

I don't know why you would bother with any of these in your vehicle. Weight won't be a major consideration, so throw in a full bag that will keep you snug and warm.

In trials in my living room, I have noticed a fair amount of condensation. Others have made the same observation. Nontheless, In a tight situation, I would welcome any of these models.