Im in two minds about mounting on rubber rings and particularly if it allows the board to wobble even ever so slightly . Any movement at all of the board relative to the crafts frame I suspect will cause oscillation and probably jitters during quick maneuvers. . I'm more in favor of adding vibration dampening pads to the arms and frame rather than suspending the AMP board. Take for example if the motors are causing a horizontal circular vibration from the motors and this circular rotation is say clockwise, then this is without doubt is going to affect the yaw if the board is moving differently to the frames yaw. So if anything I feel the oring idea is in some cases more counter productive than what its trying to achieve. The APM board in my view must be rock solid fixed to the frame to be able to quickly and accurately read what the aircraft is doing. Any compromise even if only very minute will without doubt affect the stability of the aircraft. We have to realise that if the board can be so easily affected from such small amounts of vibration and it is so sensitive, then the idea of APM board suspension mounts possibly is not a good idea
I feel some of the people having trouble with the PID tuning could be because their boards are moving and are not firmly fixed the the frames.
One method I have used to dampen vibration is to wrap a metal rod in some soft rubber and then slid this into the arm tube just under the motor. The rod floating in the rubber wrap takes quite a bit of the high frequency vibration out of the arms.
Just my thought on this.