Okay So here is the line mount test. I mounted it on a Beastmount V2, If you use a Beastmount. Be sure to tighten all screws so there is minimal to no movement in the the arms or cross bar. Changes in the mounts geometry can cause issues with the Quark.
First thing I will say, the quark does nothing for overall stabilization, but does keep the horizon level.
When using a line mount, be sure to put it on the line in the right spot. Pinching line can impact he GoPro and the stabilizer and cause issues.
Underpowered is not a good time to use the quark on a line mount, it is heavy and the lack of tension on the lines that happens from time to time is not your friend.
The quark does not like to be overhead. When using it on a line mount, I suggest you start recording when the kites is low and stop when it is low. Overhead causes a slight vibration, like it does not know where it is. Transition are good as long as they are done quickly.