I have a C315 with the Raymarine EV-100 wheel pilot. I have found that it mostly works OK. But, anytime it is difficult to hand helm the boat, the EV-100 struggles. So, under sail in light air, especially with the wind on the stern or in heavy air with significant weather helm or in very shifty winds, I find myself turning it off. Also, in bumpy following seas under motor power the EV-100 does not work well either.
On the other hand, in more "normal conditions" it actually performs rather well. I have had the pleasure of going wing on wing for long stretches under autohelm. I have considered adding a rudder sensor, but I am not convinced that will actually help. Even the people at Raymarine gave me no assurance it would do any good when I contacted them.
Would I personally spend the extra money to get a pilot that attaches directly to the rudder post, probably not.