Because of Q rings I've always used rotor chain catcher. However, I was still dropping chain once every few rides.
Although this was annoyance, dropped chain has never scratched the frame and I've always thought the chain catcher stopped the chain from harming my bike. That is until last Sunday.
I was cruising along at 20kph with very light torque on the pedal and the chain was dropped again, but this time the chain was jammed between the chain ring and the frame and scratched my beautiful S5 :(
Once home, I started to inspect the chain catcher, trying to figure out why this device that was supposed to prevent chain from dropping wasn't functioning properly. The gap between the catcher and the ring was only 1mm, but upon closer inspection I've realized that the catcher wasn't parallel to the ring but rather come in at an angle. So the gap was more like V.
Long story short, I've ditch the Rotor chain catcher and put on a k-Edge, adjusted it to be parallel to the chainring. I've went through some very wonky shifting to drop the chain on purpose and voila! K-Edge actually "catches" the chain and the chain is back on the ring.
All this time I thought the chain catcher was just there to minimize the damage to the frame once the chain is dropped.
I believe K-Edge works because 1) it has wider profile over Rotor and 2) you can fine tune the angle because it has wide bolt hole.
Only two negatives with K-edge are that it's heavier and a tad bit more costly compare to Rotor.