I had the same decision to make when I bought mine. The reduced sway control is the only difference. I read somewhere the E2 has something like 75% less friction. There is still a lot of friction since the weight of the rig forces the spring bars to rub on the L brackets attached to the camper's tongue.
Since I didn't have a problem with sway w/o one I decided to save a few bucks and get the E2. Works great. I also got the 600/6000 version - so if I move up to something larger in the future I won't have to change the WDH too. The manufacturer confirmed its ok to use a heavier-duty model with a lighter camper.
Make sure you use the online tool available on the Equalizer site which tells you which shank you need, and which holes to use. It will save you a lot of time in making adjustments.