Thank you very much for all the answers!
rmackey9, yes we (Copter Express limited) have a lot of very long logs, because actually we're developing an autonomous drone and the charging station for it, so the drone can do some job, then automatically land to the charging station, wait until the battery is charged, and then fly again. For precise landing we're using our own system, that lands drone using camera and markers.
You can check out the video of our system work if you interested: https://youtu.be/jVYJgF9WNKA.
With this autonomous system we need the copter to work really robustly, that's why we're making a lot of tests. First, I think we'll enable the prearm checks, and then may maybe we'll try to disable the internal compass, as it is not necessary.
So I'll post our results later.