The SF mixing levers break very easily , in my experience. So does the plastic flybar see-saw. I woulk say go for the aluminium.
The boom is kept in place by friction. Mine slides in a little and the belt gets loose every time i touch down too hard. loosen the 4 screws, pull the boom out again and re-tighten the screws. Not too tight, eventually the srew holes strip their thread.