style is simply one oval tip with slant cut sitting in the middle of the same size muffler (amplifier in B&B's case). I remember LRD VDR told me that the quad tips sound louder than the dual tips due to buffle in the quad tips' amplifier years ago but I have never heard of the dual in person other than seeing it once.
The dual tips' canister is basically a straight thru unit. IMO, 4.5" dual round system looks more filling in the cut out area than the dual 4.5" dual oval system while the quad 4.5" oval system fills the space the most and the overall shape goes with the bumper line better. The dual oval looks like something is missing. Hence, one of the reason I go with quad oval system.