It might be more correct to say that some of his current problems disappear, to be replaced with new ones.
Consider how the handles are restrained from moving (wobbling, shaking). The coped round tube provides a good deal of restraint, especially if the clearance hole for the screw is close fitting.
Now change to rectangular tube with a flat-ended spacer tube: the only thing stopping stuff moving about is the friction from the tension in the securing screw.
