I've been working with two types for the several weeks, the 3/4 cast aluminum (zinc?) couplings have cracked and even split apart under stress, which never happens with the steel ones.
Also, unless directly on top of it, the phillips tip bit driver always slips before it gets real tight, forceing me to put down my screw gun and use my common tipped Kline reammer to torque down the fittings.
While the steel fitting screw heads fit the bits of my srew gun well enough to torque sufficiently at different angles, they also strip out and the screw heads have sheared off entirely, where the cast aluminum (zinc?) fittings never do this.