The problem with aggressive 3D acrobatics is going to be the EKF. The problem is that our current Acro mode uses the attitude from the EKF to achieve a very tenacious attitude hold that does not drift, etc. It also gets it’s rates from the EKF, instead of the gyros directly. I have had a case where the EKF went bad in flight due to a bug in some beta code, and I was able to land it in Acro mode, but it was difficult as it kept moving around on me. In fact it was somewhat of a crash landing, I just got it over the runway about 2 feet off the ground and killed the motor.
I haven’t had a problem since that bug was fixed, but I want to caution people as, I can’t actually test the 3D performance myself, as I’m not capable of piloting those maneuvers.
What is needed, and we have talked about this, is a fall-back mode which uses pure data from the accelerometers. Something you could switch to should the EKF go bad. I expect this will happen for AC3.4, it’s pretty high up on my list.
As for the performance relative to other controllers, hard to say, I haven’t flown any others. Nor have I ever seen any kind of data from other controllers. Best I’ve seen are commentary from users about how “locked in” something feels, which is pretty subjective.
For collective control when switching modes, there really is no strategy. It’s up to the pilot to do what is necessary. If you are Stabilize mode, hovering with the collective above the center, and switch to Alt Hold, it will start climbing unless you move the stick to center. There’s really nothing we can do about this. We have thought of ways to solve it, but every method leads to other, much worse, problems. At the end of the day, it is still up to the pilot, to pilot the vehicle.
For disarming in flight, nothing can be done. If you hold full negative collective, and left yaw for 3 seconds, it disarms. Again, this is a limitation of doing extreme acrobatics with a full feature autopilot. Doing full negative with full yaw for 3 seconds should be extremely unlikely however, even with the most advanced maneuvers, I think?