I have thought about adding rudders but have not seen any flight vids or read any feedback on them.
It will be interesting to see how they go.
Mounting servos on top is not hard and there is nothing stopping you still doing it .
Just cut the original servo holes all the way through the wing and mount the plastic servo holder from the top.
The only problem is if you glued the control horns in place.
Edit. You talked me into it
Decided to go ahead and do the rudders .
Weather is not looking good here so will test fly later in the week.