There are no problems with this system, if several caveats are followed.

One bizarre thing I have noticed, on two ARFs now- one a Goldberg Ultimate, which is my current project- is that "they" tell you to hook up the pushrod at the servo end when it is offset; IOW, not centered in the fuselage. This is to allow the center servo position to be used for a pull-pull rudder control, but it also introduces differential throw on the elevator, as one side will moving farther than the other.

It doesn't take a nuclear physicist to figure this out, so I have to wonder...

Anyway, the fix is easy. Below is a pic of how I did it on the Ultimate. I fabricated a similar set-up on a H9 CAP 232 quarter scaler, but used "store-bought" components mostly- a Nelson bellcrank, DuBro connectors, etc. The one below was fabricated from stuff in my junk box. It is a bit cluttered in there, but you can see the elevator pushrod coming to the appropriate servo over the rudder pull-pull bellcrank- which was made from a Dubro heavy duty servo arm. That's how to get the necessary central location for the elevator pushrod and rudder bellcrank; vertical displacement.

I suspect the CG Decathalon has a similar set-up to the Ultimate that will need this treatment...

Just remember to keep the two sides equal in length and the bends the same angles, run the servo hook-up point in the center of the fuselage, and you'll be fine.