I haven't tried them yet, but nrs has a cheaper option for that design concept of oar blade...
I bought a pair because I'm often running boney rivers. I will try to remember to report back after I try them.
Also of interest is that these blades are quite a bit lighter than cataract magnum blades, and even a little lighter than Carlisle outfitter 6.5" blades... Even though the helix is 7.25" wide, and 2" longer at 29".
The spine of the helix blade seems to be some sort of carbon plastic instead of metal like the Carlisle. That explains the weight difference, and also means that bending a blade is unlikely, but breaking one is more possible. Time will tell on durability.