U-joint vs pot coupler

Yeah, I was sizing up the Borgeson coupler yesterday. I noted that if I want to catch both splined portions on the Borgeson steering box shaft, the set screw is not centered on the trough between the splined sections, it actually just lands on the spline section closer to the box. I imagine one wants to engage both splined sections. You can see from Syleng1's pic just above, that centering the set screw in the trough doesn't give you much engagement with the lower splined section. Thought: why use the set screw at all? If you leave it off, then this allows for the axial movement along the column, just like the pot coupler, no? There's more than 1" of engagement splines in the coupler, couldn't one just let that end float, grease the splines? No way there's enough flex for it come off, am I right?