I second Kent's comment. I also flew behind a Blue Mountain efis with integrated AP. Everytime there was an issue with the efis, the AP was effected. Any attitude problems with the efis, the AP malfunctioned. It's hard to compare the 4500 with the blue mountain (one works, one almost worked), but it gives me great piece of mind knowing that if the efis has a problem the AP will continue to function (although with somewhat reduced capability). The level of integration between the efis and AP is good and makes for a very full featured AP.

CA