Remember that Simul-Class is supposed to give Class A tone with better efficiency. So class A backed up with class AB.
Class A is terribly inefficient, sending less than 25% of the power it consumes to the speaker. So it can get a bit anemic. Class AB is more efficient, so it can provide more power to the speaker without having to run super-hot.
In the actual implementation, both sections are actually class AB, but one is running hotter, closer to class A. That hotter class A-ish section is also giving less power to the speaker than the cooler class AB section.
IMO:
The hot class A-ish section gives a looser feel with more linearity. The cooler class AB section gives tons of power for big low-end, but also more harmonic content, including some less-desirable harmonic structure.
So for me, the class AB in, say, a JP2C, is nice because it gives a tighter, punchier tone and huge dynamics. In my Electradyne and the Mark V it gives a bit more sag and looseness, at the expense of some dynamics and stiffness.