To avoid confusion, I ought to preface this post by mentioning that I began tests quite some time ago with the APM2 purple board. Since then I've gotten my hands on it's older brother the APM1 (hey, they're cheap now and then!). I have the APM2 in my heli now, so I decided to throw the APM1 on my quad in place of the APM2 to see how things compare...
So that might be a bit of an excessive title, but if I didn't know the differences between the two boards, I would claim that the APM1 is superior to the APM2!
A lofty claim, you might suppose, but let me explain why.
Firstly, the yaw issue I had with my APM2 is completely gone after installing the APM1. I'm using the same quad frame I had my APM2 on. Perhaps shuffling the ESC's around a bit helped. I moved them a bit farther away from the center and they now reside near the motors themselves. I've heard that to be a good thing, and I've heard it to be a negative thing having long + and - wires, so who knows.
The most surprising observation I made was with regard to loiter. This is the first time I've gotten anything to loiter. I can't claim to have even once gotten my APM2 to loiter, but right off the bat with default parameters, the APM1 on my quad loitered amazingly well (both using 2.5.5). Why? I have no idea. I didn't run a long test, but take a look at the results in the picture. The longest distance traveled was about 7 meters. There was a slight breeze. I suppose this warrants some careful comparisons of mounting, wiring, etc. for me in the future.
Anyway, that was my surprise for the day. I know the APM2 board is quite an improvement upon its predecessor, and I'm really not claiming otherwise. I suppose all I'm doing is pointing out the causes for my sudden onset of confusion and hope. Either way I'm happy. I have an APM1 in my plane, APM1 on my quad, and APM2 on my heli. No complaints here (except crashing the plane repeatedly, but that's another story...)