An impact driver has snapped the head off of every seized screw or bolt where I've tried it. It isn't that hard to snap a screw head off even while the screw is advancing through hardwood or fiberglass. I've done that too many times to admit!
I find that if I can't take a screw or bolt off with a hand driver, I'll snap it off with an impact driver or even a fairly compact box wrench -forget the leverage bars! I think heat is best method for loosening - then
very modest persuasion with an impact driver. I don't have any patience for the liquid concoctions.