Half the effort
Twice the fun!
Half the paddle, twice the paddler 
I started this thread as a joke, not thinking anyone would actually buy one of those things…sorry Dave, couldn’t resist.
I like bigger drip rings on double blades to keep as much water out of my canoe as possible. I’ve tried a 250cm and for me, in a 28" canoe, that’s just enough to keep the blades just outside the gunnel and still get a good powerful stroke. I’m using a 280cm double blade when soloing tandem canoes that are 36" wide. That’s actually a little too long, and I don’t double blade tandems very often, so I’m going to cut that paddle down to 260cm which should be just right for my solo canoes. If you keep the blade outside the gunnel, using a low angle stroke, there’s very little paddle drip into the canoe.
Some paddlers say that long double blade paddle is inefficient because it swings the canoe back and forth with each stroke. That’s true if you haul the stroke all the way back past your hip. If you paddle like kayakers, power stroke from the toe to the knee the yawing is not as pronounced.
You never know
Dave may like the drip rings so much, we’ll have to have a drip-ring comparison at Raystown next year.
Thanks for the support, Ness
As noted above, I don’t have high hopes for the drip rings being the second coming. Purchase was just a way of relieving boredom while sick.
As for a Raystown comparison, why not compare something of interest to more, such as single malt scotch.
Dave
HUGE Macallan’s fan here . .
. .so i’ll drink to that!!!
Single blade
I don’t use double bladed paddles in canoes.