Cornfed did a good job of answering some of the questions about the heater Body Suit, but here's my take on it..The Heater Body Suit weighs only six pounds and rolls up into a compact bundle which you can carry using the built-in backpack straps, or in a seperate backpack like I do. (The ULTIMATE backpack sold by the same company is ideal for this)
I dress in medium weight clothing for the hike into the stand so that I do not get sweated up. Once you are wet, your odds of staying warm on stand in cold weather are near zero! (Remember, you still have to get to/back from your stand and you may have to track your game, so don't dress TOO lightly for the conditions when you are out of your suit either)
Once I am in my stand and SAFELY HARNESSED I slip on the insulated booties right over my boots, step into the Heater Body Suit, and zip it up. By wearing a neck gaiter and warm hat, or a full facemask that tucks into the neck opening I am completely sealed from the outside cold.
Like a giant mitten/sleeping bag, your body heat is contained inside a windproof, chamois lined cover which will unzip silently and fall free from your shoulders w/ little movement and no sound, and not interfere with your shooting at all.
I've used while bow & gun hunting and it has never cost me a shot yet, and while yes- it is expensive, I never would have been able to take the shots I have taken out of it had I not been out there, and to me that makes it well worth the money in the long run!
Don't forget too, If it doesn't keep you warm....they'll give you your money BACK!!