I just re-fitted my new to me Monty 15 with an IDA rudder and combo mast crutch assembly. I am sorry I did not use the stock rudder to give you a better comparison and the reason for my switching was more about trailering convenience of not removing the rudder assembly and having the mast crutch bolt on simply by removing one screw set assembly. Now that I have the IDA rudder I can appreciate the UP/Down mechanism and so far the blade has performed wonderfully. It seems like a very nice upgrade but my feelings are I could not compare performance to the old one and my performance comparisons would have needed to be done in strong winds when you'd expect rudder stall anyway. Good luck with your decision to change, I am very happy with mine. Smiley M 115 #616 Another Wrinkle. Smiley magoo252@comcast.net