The difference between the two leg engine guard and the 3 leg engine guard is one leg.
The two leg variety bends the frame mount tabs in a crash/rollover. I believe they are considered "sacrificial".
The three leg variety does not bend in most mishaps. In order to bend the three leg variety, the frame and engine will have to distort. I hope you are not on the bike when that happens.
The three leg also has a different main support profile where the forward end stand proud farther than the rear. I think that is more art than function, though.
Dunno, is that "much difference"?
Hey, I found a pic of them installed!