Hey,

I only use the adjustabe servo arms for my throttle. I wouldn't use it on a primary flight control because i always like a fail-safe system. With the fixed servo arm, if the screw comes out, the servo arm should still stay on the servo because there is some force required to pull it off the servo. With the adjustable types, if your screw goes, so does the sevo arm. The only primary flight control i would put it on is the rudder, because you can fly without it.

You never no, it might save your plane one day.

Cheers