In my limited Boeing experience (737 various) it is a 'typical' Boeing auto-throttle ie it does not react well in turbulence and is rubbish at speed control near the BP.
I was once told the turbulence symptom is due to the input from the alpha-vane which bounces around in turb, and the poor speed in descent is due to excessive 'smoothing' of the system to avoid 'chasing'.
Best to use CWS or manual near the BP in my experience.