The foot pocket on the Eddy is a better shape than my Slipstreams, so they are more comfortable, as they are designed to fit an actual foot. My slipstreams started to develop a crease in the middle of the foot pocket due to the shape of the design (the OMS is sort of a reverse taper), which I actually found kind of odd.
The specific gravity on the Eddy is at .9, so they are neutral to positive depending on freshwater vs salt. They are very lightweight, and I would say they are at the proper stiffness/flex for what most people want. In comparison to the Slipstream they are about the same on the flex, not much stiffer/softer in either direction. I do not have mine on hand though at the moment to give you a direct test of them versus each other.
Hope this helps!