Very nice model - Good looking render.

For me the dials, cable and mouth peace look unfinished, shaders wise.
Is there a reason they are white ???

Looking at some ref (as I never seen one of these before) the dial are usually a chrome color with the mouth peace being Grey/Black over the different models, but could not find the one you modelled.

Again just its just what I think looking at it - The other shaders and model it self look spot on.

As for depth and AO - There is no harm rendering them out and playing with them as it would be good practice.

Tweety