As has been said, people have been warm to way below zero ( with augmentation that I think is quite easy, even some with little or no augmentation
) or toasty at 14F no tarp in a 6F windchill ( me, by adding a fleece jacket and down vest I was not sleeping in, plus the sweet HH kidney/torso pads) or just barley warm enough with the basic system (1 space blanket, one HH OCF pad and under cover) at about 30-32F. And some others have not been happy at 50F, and some have had condensation issues.
I grew to love mine, even though I am also a big fan of my Speer PeaPod and JRB UQs especially used on a JRB bridge. I have had as many as 3 HHSSs ( 2 now ). And there are quite a few others like me around here, but there are also the ones who have no use for it. IOW, you will never know by asking opinions around here, they are all over the board.
I agree with those that say for about the same price you can get an AHE Climashield UQ which will probably work like a charm. But it will not pack as small, probably won't be as easy to boost/augment unless you add a ccf pad, and will require a bigger, heavier tarp (or an UQ protector) for as much protection from wind/rain/snow as comes built into the HHSS. Pros and cons, but a these UQs are another great option at about the same price.
Wow, I sure had no memory of this old thread! In it kwpapke is seeking advice about how to extend the HHSS by adding his Parka. Shug chimes in to say "maybe we can get together for some cold weather testing". Next thing you know comes the uber famous minus 27 hammock hang video of Shug, who was joined by kwpapke with his augmented HHSS! This thread was preparation for hammock hanging history!