As far as scent goes I haven’t noticed any deer or elk being bothered by my using them.
I found an excellent way to wear the hand warmers is to safety pin one over each kidney on the out side of my under layer (t-shirt). All your blood has to go thru your kidneys and it is an efficient way to circulate the warmth. I have been toasty warm while elk hunting in the coldest weather in MT and pass this on to all my friends.