OK to use? You bet.

The design is almost foolproof. Keep the screw tight and no way for it to fail. And the screw goes into grippy material and can't vibrate loose so what's to fail. And the material in the arm's parts is good stuff.

You bet.

The only drawback is that it gives newbies a way to rig the servo with a long or longer arm and the first choice should usually be to use the shorter arm on the servo when possible.