As the co-owner of C-320 with a 4000+MkII I would say that they are adequate, but not great and it isn't simple or necessarily inexpensive to get one up to 'good'. Ours works great under power in relatively calm water...but we don't use the engine much at all. I have been frustrated by its excessive and somewhat sloppy response (and yes, I have done all the recommended programming) under sail. I have even acquired the rudder response sensor, but the installation is so onerous, that I keep putting it off to go sailing. The bigger problem for us is I sometimes don't go sailing in heavier air because it is just too much work tacking when the AP is not working well.
I think from what information that I have been able to glean, that the new generation of Raymarine underdeck autopilots may be the way to go if you want simple, reliable and good to great performance. Obviously, that is not inexpensive. I may bite the bullet in the hopes that it will get me out on the water more, but that is still a question for me for now.