These aren't true 4 into 1 systems. They're 4 into 2 into 1 like the MV. The only difference is the MV goes from 1 back into 2 (presumably to allow sufficient noise deadening volume without resorting to a huge cannon sized muffler). Once the system converges from 4 into into (2) or (1), the final silencer configuration makes little difference in performance (provided it isn't excessively restrictive).
A true 4 into 1 usually means a little higher peak output at expense of powerband. A 4 into 2 into 1 gives a wider powerband but sacrifices peak output. Most people will opt for the wider powerband unless they're just benchracing and talking peak dyno numbers.