RE: Improving stability
Here are the two gyro's I am going to experiment with for the Catalina Kadet, the one the left is one of those orange things and it is three axis, cost about twenty bucks. I don't deal with Hong Kong so a bud picked it up for me When we were experimenting with our wireless buddy box setups. The one that my LHS just dropped off today (oh man how many LHS deliver?) is the the new Eagle Tree three axis and cost about seventy bucks.
Grey beard the problem I beleve you experianced and the need to turn the unit off was simply the result of running to much gain. My experiance with the Quad did not require turning the unit off and in fact that old Hobbico cannot be turned off. The gain required for keeping the airplane striaght on the runway require only a rather small throw of the rudder. The advantage is the speed of the units response before the human can even detect the yaw.
If the gain is set to high when used on rudder there will be some dutch roll detected in high speed flight and the solution is to just reduce the gain. The Quads unit is always on and you really cannot tell.
John