sway control devices are nothing but a compensation for a imporperly loaded trailer. yes I like some of the saftey features being built into trucks now days but as it was mentioned before that is for regaining controle once the sway starts in an atempt to minimize the risk to life if it has gone to far.
the best way to prevent sway id to load the trailer properly with 10 to 15% (for conventional tow) of the total trailers weight on the ball. if your hitch is rated for 1000 lbs you dont need a equalizer to tow 700lbs, it wont help with sway much, but it may make the ride a little more confertable by reducing the forward/backwards rocking of the truck and trailer every time you hit a bump or dip in the road.
in 39 years of towing I only ever had sway once and it was my own fault as I had less weight in the front to make it easier to load on the truck (front jack was broken) after that trip the jack got fixed and it was always loaded properly.