Does EDA tell you something different than measuring heart rate or heart rate variability?

Yes. The heart is innervated by the two main branches of the Autonomic Nervous System: (1) The Sympathetic Nervous System (SNS), commonly known as the “fight or flight” system, and (2) the Parasympathetic Nervous System (PNS), commonly known as “rest and digest.” Most organs in the body are innervated by both the SNS and PNS. In order to measure the “excitement” or “arousal” dimension of emotion, the signal of interest is the SNS. The skin is believed by physiologists to be the only organ purely innervated by the SNS, making it the best bodily measure for what “revs your engine” or activates you. (Note: while SNS is often called the “fight or flight” system, it activates also with positive excitement and anticipation.) Scientists currently do not have an accurate way to isolate SNS from measures of the heart.