Oh, yeah, it does away with the angular misalignment and steppers rocking on (or with) the mounting plates.
But you still get some eccentricity between the motor shaft and the threaded rod. Not initially, but as the sleeving gets squeezed/torn, and you keep tightening the set screw (or the clamping screw), the layers of sleeving can become uneven. One caveat, though - i had to use 3 layers to get to the wanted diameter, so your mileage may vary
BTW, i found a nice, simple way to align the rods to the motor shafts. Mount the coupler on one of the steppers and unscrew the rod out of it so it hangs above the coupler. Poke the threaded rod with your finger a little, get it to hang loosely (which it will, unless your delrin nuts are unused, because the threads do wear out rather quickly initially). Unscrew the stepper plate T nuts a little - enough to move the stepper freely, but leave it tight enough so it keeps position. Look down the threaded rod and see where the end... ends. And move the stepper along with the plate and the coupler until the coupler hole is dead center under the rod end. Tighten the stepper plate (carefully, while watching the rod, so you don't rotate it away again with your wrench), screw down the rod into the coupler with your fingers and tighten. Rinse and repeat for the other side.
Edit: Obviously, you need to have the coupler on the other side too while doing one side, but the point is, it doesn't have to be perfect, you just need it to keep the gantry up. Also, it helps immensely if you adjust the gantry so it's level and immobilise it while doing this, becase there's usually enough leeway in the left and right Z to have it at enough of an angle for the threaded rod to end up hanging at an oblique angle.