Phil this is the stuff I use. It is 2-56 rod. It is plenty for your application. The key to using any of these is to support it at regular intervals. If you are using a golf club for a fuse then use a zip tie every 2"-3" all the way back. This will keep the flex out of the system.
It was common 15 years ago to see the flex rods used any many planes. At least around here it was. The guys would run it through the fuse for the elev and rudder. But they would only attach the outer tube where it exited the fuse and right behind the servos. I stuffed a friend Corsair for this very reason on the maiden. The rod would pull the elev down no problem,but it would not push the elev up once the plane got some airspeed.
Also, you can use the plastic like in your pic and make it better. Instead of using the supplied threaded couplers. Get some 12" rods threaded on one end. You can cut these down to three inches or whatever and use them. Just put the unthreaded end in the tube first and push it in till you can thread half of the threads into the tube. Then put the clevis on the half of the threads left sticking out. This adds a little weight but takes some of slop out of the nyrod.

David