We have had hidden systems for years. I still have a couple in my shop but I have only used them on a true scale plane. I have seen a newer system that kind of torques the control with a joint and bent control arm, fully hidden. I have used a lot of torque rods and they work fine, I just don't use them these days. Can't recall ever having any real problems with them either. I have seen an aileron servo lock up on a two servo set up while the plane was doing a roll, the plane wouldn't come out of the roll and went through a five strand barb wire fence so I know the two servo system isn't fool proof either.
As my instructor told me, it's your plane, you can do anything you like to it. We used torque rods for a lot of years and they work. I just no longer use them so I voted never.