i have used the standard non-zip snugpak bivvy which i think is the same as the special forces one other than not being zipped (has a simple hood), have also used hunka standard and army bivy bags, snugpak is the lightest and smallest packing of the three, seems longer than the hunka and about the same shoulder width, seems to breathe well enough i have only had condensation in it on one occasion on a very damp still warm night but the condensation was excessive wetting sleeping bag badly, used on wet windy nights it has performed okay (the wind seems to have been the factor) seems to be waterproof enough (hydrostatic head of 5,000, hunka is double at 10,000), i prefer the hunka myself as it fits me better (i am short and stocky) even though it is marginally heavier and very slightly larger pack-size, the night i suffered bad condensation might equally have happened with any other bivvy bag it was a particularly damp night, i don't think there is much difference in performance between the snugpak and hunka, though if access is a priority the zipped special forces bag wouild be easier to get in and out but the zip might possibly be a weak point in waterproofness.