Personally, if you don't plan on using or needing the ES then I would get it the hell off of the bike. They are a weak problem design that will eventually fail. Pretty much guaranteed. As Mazza said, they sell primary covers that convert from ES to KS only.
You do not have to use the ES for it to ruin your day and your bike. The sprag only turns in one direction. A backfire, a misfire, or hiccup during a kick start can jam the gear. Best case it damages the spag, worse it locks up, and worse yet it shatters and takes the case with it.