True. Any reaction you have would be on automatic. You'd be dodging at least as fast as humanly possible. The spider-sense doesn't just warn you of danger before it happens, it also takes control of your body (almost like it has a mind of it's own) and forces you to move without even thinking about it.
Yep. It is even able to tell you the exact direction the danger is coming from. It can tell if your lieing and sense your everymove all the way down to the heart beating in your chest. Spider-sense does all that and more.