I'm going to take a different tack. I had our AP put in in '16 so I don't have any meaningful numbers.
Installing an AP is a real project as it includes a NMEA network, as well as all the wiring and pressure hoses, presuming you want to overlay radar, ais, depth on your chartplotter (CP). That also means that your version of CP will support that. With Garmin you need an XSV cp.
We did an 8yr Loop and the cp/ap steered 98% of the time. Wouldn't want to have hand steered that so I think you will appreciate the addition.
Any specific questions, let me know.