From what I heard of the HGS used on Embraer 145s -Rockwell Collins- is that it is extremely accurate in tracking, trends (speed etc) are displayed more accurate then on the PFD and if you're getting out of any limit, the whole thing blanks with a big warning displayed on the HUD. Meaning that you fly it properly down to the runway, or the system will not guide you. So in this way, you would not be able to have overspeeds, excessive ROD etc. Don't know what is being used on the Dash, though.