Hmm, okay. I couldn't find any other measurement of this headset, so I will leave it up to the air whether it is representative of the headset, then. Certainly the noisy/spiky character of it should be discarded as a measurement artifact, but the other curve parts going up and down in it might be real. The ideal group delay plot is just a flat line at 0 ms that gradually rises towards the bass due to inevitable high-pass filtering somewhere in the amplifier or such.