Bent shaft paddles are good for speed if you use the stroke and switch method, but are not so good for any other strokes. My uncle swears by his but he only travels lakes. On a river they are not as efficient for all the complicated little strokes you need to zig zag around. Their true purpose is for canoe sprinting; like in the Olympics, and I am not sure why the average person would want one? I make paddles part time for a sideline and have experimented with a number of different blade types. I find that a long thin blade is the most efficient as it doesn't tire you out as much as the bigger paddles. You don't get that initial burst of speed but I find that a short swift stroke with a smaller paddle soon has me zooming past everyone else who it tired out from their monster paddles. If you want to race across a section of flat water there is no denying the power of the bent shaft though, they may take a lot of calories to use but they apply maximum power to the water at the most critical part of the stroke. There is an interesting article here that covers that.