There’s more lightweight shelters to choose from but, as a former bivy sack user, it looks like OR did their homework on this (ample skeeter net, built in “sombrero” for rain ... probably dorky but who’s going to see you in the rain?). A one bivy piece has merit in some situations, such as crowded PCT campgrounds. Just find some decent ground to plop it down while everyone else mucks about looking for a bigger area, or are staking bunches of guylines as the wind blows the shelter down. The colder the better for bivies, but hotter weather sucks. If the bug net can stay taut, maybe that alleviates heat concerns? Bivy sacks are not for use in grizz country though (see burrito comment).