None of it really is acceptable, Dan. But you’re right, the box will be fibreglass or plastic at best…. The screw won’t be holding anything.
It’s an older thread now… so I don’t know what became of it all.
These boxes tend to only allow holes on the bottom side, where there’s a marking. Maybe fixing holes for screwing into brick…. But I believe they are supposed to be held in with mortar when building the wall.