Demunseed reminds me of the drunk who thinks he will never get caught driving home from the bar because he takes the back roads, then one night he goes in the ditch.
I wish I had a dollar for every person at DIY with compass errors that turned out to be the FC was mounted too close to the power wires, and even ferrous screws tightened with a magnetic screw driver that magnetized the screw. Then others that calibrated their compass too close to a steel building or underground re-rod etc. Oh, did I mention countless crashes due to compass errors? The guy in the video is a dope for telling people to fly anywhere they want. Will he pay the guy that took him seriously and wonders why he loses control of his copter?
Below is a video I made it to show just what happens when EMI can adversely affect the compass. It may take 100 flights, or 10, but at some point if a pilot flies with abandon paying no attention to possible EMI that can cause the copter to go nuts, their luck will run out. Now shielding against EMI is a different story.
I took the P4 to work to calibrate the IMU on a level CMM surface plate and discovered very high EMI. Notice the warnings.
First at the back of the machine, then placed on the floor:
Again at the front of the machine where the compass interference went off the scale, then placed on the floor: