jmx66,
we use coupler identical to the one, you showed, we use them on 10 to 20 ft/lb, powered 90 degree actuators, we find unless they are keyed to the shaft, they will slip. The other option, for us, as the coupling is enclosed, we drill the coupling, and drive a roll pin into the coupling, through into the shaft. Leaving about 3/16"-1/4" of the roll pin sticking out, so it can be removed (we drill into the shaft, but not through the shaft).