Jan
My 3.75kg octo was very difficult for me to setup probably because of the many autopilots I have tuned over the last few years. I thought that the octo would need big changes in the attitude PIDs to get it working right. My biggest surprise after a lot of testing and crashes was that default settings worked, except for rate D needing to be reduced. The octo now has great performance in missions and position hold. For me how the octo performed in manual mode was not a good indicator of how well it would perform in other modes.
To get the octo to fly with defaults vibration had to controlled.
Larry