I noticed that the ordering options for APM 2.0 in the diydrones store have changed. You can order the APM 2.0 with either the GPS or the magnetometer (but not both).
I got the Sonar Sensor today and tried it out. I first tested it. It shows 35 cm from 0 to 35cm and then onwards seems pretty accurate to within a couple of cm.
Altitude hold was a lot more precise than just Baro.
Today I had a mishap (thankfully recoverable) with my Arducopter. Here's what happened. I engaged ALT_HOLD and for a while it held altitude and then slowly began to climb. I don't have sonar, just baro. In trying to bring it down, I lowered the throt