Have no experience with the Warm Bag, but have hunted with the HBS for at least a decade. It is, hands down, the single best "accessory" I use while hunting. It makes all day sits in November in Northern Michigan not just bearable, but completely comfortable.
I have no problem using it with traditional gear. It adds a small bit of movement/time to get out of the bag, but it's never cost me a shot. I'm convinced that there is added scent control in being enclosed in the bag and it also masks any movements inside. I can move my hands, wiggle my feet, etc. with little discernible motion on the outside.