I have an IWOM suit. I picked it because it had free arms with sleeves. I hunt mostly climber stands so its a bit tricky to get into after the climb, (it even has a rear slit for your safety sling, you wear a harness under and the tether easily slips through a slot made for it) but on real cold days there is no equal. It is surprisingly light for its warmth. the legs are basically just a bag, but it keeps feet warm and all. Feet were my main cold region and huge boots, or hotpacks were a staple. Its made so you can stuff sack it, or wear it compressed around your waist for the pack in. you can wear substantially less layers and garments underneath once you get into it, so for me, cold day overall carry in pack was lighter.(with the suit) Its very well thought out with pockets and pouches throughout. you can walk in wearing little to keep from sweating, then just this one light layer, well sealed and you will be amazed at the sit all day comfort. Pricey, but the effectiveness will surprize you. each system is a bit different, so you have to research and decide what suits your style best.
I only use it on the coldest days, but its one purchase I am happy with. no regrets