I did fine at 10 to 14 degrees on a windy day for twelve hours a couple of times this year and that was sitting in a tree stand the whole time. Put a digital thermometer in the bag and checked it a few times; it maintained 59-60 degrees the whole day. I had to keep my water bottle inside the bag to keep it from freezing.
I wore a thin set of x-scent base layer, two pairs of walmart thermals, regular ASAT pants and shirt (cotton), and a light jacket. I used two large hand warmers on my kidneys, two on my knees (knees always get cold), and two small warmers in my shirt pocket (old farts setup; yours may vary). This may sound like a lot, but it is the same thing that I wear with the HBS under these conditions, and it is just enough to get to my stand tree without freezing or overheating in these temps.
I also wore two layers of socks with 800 gram boots. A Loki head cover and thinsulate hat.
As stated this is the same thing I have to wear with the HBS system. Plus with the HBS, I have to put on the heavy boot covers that come with the HBS.
Results, I did feel more comfy in the Warmbag. It is lighter weight than the HBS, but uses dynamic thermal layer like Arctic Shield clothing (which is pretty good stuff, but bulkier and not near as warm as the WB). Plus the WB is waterproof; my HBS is not.
I had my doubts when I got the WB at the beginning of season, but the end results changed that.
The WB is lighter (easier to pack and carry). It is ten times easier to put on in the stand. It is a little more restrictive for my feet due to the fact that I am cocooned in a big bag instead of having legs and feet like the HBS, but it is manageable. As with any hunting product, practise makes perfect.
My feet stayed warmer in the bag than the HBS, and I did not lose heat when I was preparing for a shot like I did in the HBS. Plus, you can sit with your arms out side of the WB for extended periods of time and stay pretty warm till your arms get cold; this is impossible with the HBS. When you unzip the HBS, all of the heat inside leaves out through the opening; by only opening the arms of the WB, most of the heat stays near your core (chest area).
The WB seems a little noisier than the HBS, but I never got busted moving or unzipping the WB even on a 120 class 3.5yr buck that was 8 yards from my stand during bow season.. I nailed him. Noise is the only complaint I have heard from WB users, but I feel that it is only loud because the user is in such close proximity to the bag sort of like tapping on your skull with your finger seems loud to you, but no one else can hear it. Just unzip slowly or while deer are walking (same as with anything while deer hunting) and fuhgetaboudit.
I used the HBS for three years, but I will only use the WB from now on.
One other thing that I feel is important. The Warmbag is UV free; the HBS is a UV glow machine. The folks at HBS have been asked to not use UV brighteners in their fabric, but they refuse to go this extra step and tell folks requesting this that they don't care to do it because it doesn't matter. Been hunting for 35 years and can tell you it DOES matter in low light (dawn and dusk). The fact that they don't care about this and that the WB folks do, speaks volumes about the products.
I killed five deer this year while wearing the WB (two mature big 9 pointers 3.5 and 5.5 years). Only lost one doe because I couldn't find the arm exit zipper string with gloves on, but that worked out because by the time I found it, I had a big 9pt, which showed up after she got out of bow range standing under me at 8 yards... as stated, I nailed him, so it's all good. Hint: practice using the WB a lot to become familiar with it.
Got mine the only place that I think you can find them, thewarmbag.com . The WB cost less than the HBS, too. Got a pic of my 9pt mentioned earlier in their trophy room, too.
Sorry so long, but I think you get the picture.