6DOF vs 9DOF IMU

Hi all,

I've been looking into IMU's for my quadcopter project and am currently thumbing between two different IMU's to scope out the potential differences.

The two items i'm looking into currently are 6DOF Razor IMU and 9DOF Razor IMU

Other than the additional 3DOF provided by the onboard magnetometer, is there any difference between the two in terms of the onboard processing? I see the 9DOF IMU has an onboard ATmega328 which processes the data so I assume that the outputs will be 'clean' rather than having to roll my own data collation and parsing?

I also assume that a compass/magnetometer would be rather handy for my project (a quadcopter) as opposed to purchasing a separate unit? I guess that the all in one package will be more tuned to compensating the outputs as mentioned here.

Finally, the 6DOF makes no mention of AHRS whereas the 9DOF states that it is "AHRS compatible". Even with the 6DOF, would it be possible to roll my own AHRS setup or would it make more sense to simply buy the 9DOF module instead?

Sorry if the questions are quite vague, i'm trying to wrap my head around what hardware I need to create a stabilization system for my quadcopter. Any help anyone can provide would be greatly appreciated!

Thanks for reading!