from this link
Posted by: kayamedic on Dec-11-12 1:18 PM (EST)
ZRE includes in the blade length the skinny part of the paddle not just the fat part
I am thinking that the intent is to allow a really good vertical stroke close to the boat. Most likely the slender part of the blade allows clearance of the hull before the fat part of the blade has a chance to hit it.
Intended to be used for hit and switch and not slicing the philosophy seems to be that undue agitation from a round shape in the water is not a factor. But that may not be the way that you plan to use the paddle. Straight shafted paddles seem to go with kneeling paddlers who are also inwater recovery paddlers.